Abstract:
A harpoon breaching tool that allows security officers, SWAT teams, police, firemen, soldiers, or others to forcibly breach metal doors or walls very quickly (in a few seconds), without explosives. The harpoon breaching tool can be mounted to a vehicle&#39;s standard receiver hitch.

Description:
FEDERALLY SPONSORED RESEARCH 
     The United States Government has rights in this invention pursuant to Department of Energy Contract No. DE-AC04-94AL85000 with Sandia Corporation. 
    
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     None 
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to a method and apparatus for making rapid, forced entry into a structure, such as a door or section of wall. 
     A need exists for police, firemen, SWAT teams, and security officers to breach doors or walls very quickly (e.g., in a few seconds). Many types of forced entry tools are commercially available, e.g., cutting saws, spreading tools, explosive devices, “burning” devices, etc. However, these devices have their own inherent problems, such as noise, time-delay, fire hazard, close-proximity of personnel, etc. 
     SUMMARY OF THE INVENTION 
     A harpoon breaching tool that allows security officers, SWAT teams, police, firemen, soldiers, or others to forcibly breach metal doors or walls very quickly (in a few seconds), without explosives. The harpoon breaching tool can be mounted to a vehicle&#39;s standard receiver hitch. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form part of the specification, illustrate various examples of the present invention and, together with the detailed description, serve to explain the principles of the invention. 
         FIGS. 1A-1C  illustrate a first example of a method of breaching a wall or door using a vehicle-mounted harpoon breaching tool. 
         FIGS. 2A-2D  illustrate another example of a method of breaching a wall or door using a vehicle-mounted harpoon breaching tool. 
         FIG. 3  shows a side view of an example of a harpoon breaching tool. 
         FIG. 4A  shows a side view of another example of a harpoon breaching tool. 
         FIG. 4B  shows a side view of the harpoon of  FIG. 4A . 
         FIG. 4C  shows a cross-section view looking at the end of pipe  12 . 
         FIG. 5  shows a cross-section side view of the harpoon of  FIG. 3 , after penetrating door  6 . 
         FIG. 6A  shows a cross-section top view of another example of a harpoon tool. 
         FIG. 6B  shows a schematic side view of  FIG. 6A . 
         FIG. 6C  shows a cross-section view through the hinge pin  16  as viewed from the end of tool  10 . 
         FIG. 7A  shows a picture of a prototype harpoon, mounted on a trailer hitch of a truck, in the un-released position. 
         FIG. 7B  shows a picture of a prototype harpoon, mounted on a trailer hitch of a truck, in the released position. 
         FIGS. 8A and 8B  show pictures of the same harpoon as  FIG. 7 , with the collar slid backwards, and the blade released. 
         FIG. 9  shows a cross-section side view of another example of a harpoon tool. 
         FIG. 10  shows a cross-section side view of another example of a harpoon tool. 
         FIG. 11A  shows a cross-section side view of a spring-loaded, two-blade harpoon. 
         FIG. 11B  shows a cross-section end view of a spring-loaded, two-blade harpoon. 
         FIG. 12  shows an isometric view of an example of a harpoon support shaft. 
         FIG. 13  shows an isometric view of another example of a harpoon support shaft. 
         FIG. 14  shows an isometric view of another example of a harpoon support shaft. 
         FIG. 15A  shows a top view of another example of a harpoon breaching tool. 
         FIG. 15B  shows a cross-section side view, A-A, of the harpoon of  FIG. 15A . 
         FIG. 15C  shows a cross-section top view, B-B, for an alternative construction of  FIG. 15A . 
         FIG. 15D  shows a cross-section top view, B-B, for an alternative construction similar to  FIG. 15C . 
         FIG. 16A  shows a cross-section side view of another example of a harpoon breaching tool. 
         FIG. 16B  shows a cross-section side view of the example of  FIG. 16A . 
         FIG. 17A  shows a cross-section top view, A-A, of another example of a harpoon breaching tool. 
         FIG. 17B  shows a cross-section side view, B-B, of the harpoon of  FIG. 17A . 
         FIG. 17C  shows a cross-section end view, C-C, of the harpoon of  FIG. 17A . 
         FIG. 18A  shows a cross-section side view of a trailer hitch adaptor. 
         FIG. 18B  shows an isometric view of a trailer hitch adaptor. 
         FIG. 18C  shows an isometric view of a harpoon shaft mounted to a trailer hitch. 
         FIG. 18D  shows side cross-section view of a harpoon shaft mounted to a modified trailer hitch. 
         FIG. 18E  shows side cross-section view of a harpoon shaft mounted to a modified trailer hitch. 
         FIG. 18F  shows side cross-section view of a harpoon shaft mounted to a modified trailer hitch. 
         FIG. 18G  shows a cross-section of another embodiment of a harpoon mounted to a trailer hitch. 
         FIG. 19  shows a side view of an adjustable-height triangular adaptor bracket. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1A-1C  illustrate a first example of a method of breaching a wall or door using a vehicle-mounted harpoon breaching tool, comprising:
         a) mounting a harpoon breaching tool  2  to the structural frame  9  of a vehicle  4 ;   b) driving the vehicle  4  towards the wall or door  6 ;   c) impacting and penetrating the wall or door  6  with the tip of the harpoon  2 ;   d) releasing a pivot blade  7  and hooking the inside of the wall or door  6  with the blade;   e) reversing direction, and driving the vehicle  4  away from the wall or door  6 ; and   f) pulling on the hooked harpoon tool  2  with the vehicle  4  with sufficient force to pull out the door  6  or a section of the wall, thereby breaching it.       

       FIGS. 2A-2D  illustrate a second example of a method of breaching a wall or door using a vehicle-mounted harpoon breaching tool, comprising:
         a) temporarily attaching a harpoon breaching tool  2  to the structural frame  9  of vehicle  4 ;   b) attaching a bundled, flexible connecting member  8  to the harpoon  2  at one end and to the vehicle&#39;s frame  9  at the other end;   c) driving the vehicle  4  towards the wall or door  6  ( FIG. 2A );   d) impacting and penetrating the wall or door  6  with harpoon  2  ( FIG. 2B );   e) releasing a pivot blade  7  and hooking the inside of the wall or door  6  with the blade;   f) reversing direction, and driving the vehicle  4  away from the wall or door  6 ;   g) as the vehicle is driving away, contacting the released pivot blade  7  with the inside of door  6 , and then detaching the harpoon  2  from the vehicle&#39;s frame  9  ( FIG. 2C ), whereupon the flexible connecting member  8  falls slack;   h) when the moving vehicle  4  eventually snaps the flexible connecting member  8  tight ( FIG. 2D ), the vehicle&#39;s momentum applies a large impulse force to the door  6  via the harpoon  2 , thereby pulling out the door or breaking out a section of the wall.       

     The flexible connecting member  8  may be, for example, a chain, a towing strap, or a steel cable. If necessary, after the first impulsive force has been applied, the process can be repeated, i.e., reversing the vehicle, backing towards the door or wall to create slack in the flexible connecting member, then driving forward again and applying another impulse when the flexible connecting member snaps tight; and repeating this as many times as necessary until the door or section of wall is breached. 
     Examples of structures that can be breached include metal doors, wood doors, concrete block walls, commercial building wall construction, brick walls, wood frame walls, etc. 
     In one embodiment, a harpoon breaching tool may comprise:
         an elongated support shaft having a front end, a back end, and a centerline;   a sliding collar disposed for sliding along the shaft;   a pivot pin oriented perpendicular to the shaft&#39;s centerline; and   a pivot blade pivotally connected to the front end of the support shaft by the pivot pin; and   a tapered tip for piercing through a metal door or wall and making a penetration large enough for the pivot blade to pass through;   wherein at least some of the blade is disposed inside of the shaft when the blade is held in an un-released position by the sliding collar; and   wherein the blade can pivot outwards through a longitudinal opening in the support shaft when the sliding collar has slid sufficiently far towards the rear end of the shaft so as to release the blade.       

       FIG. 3  shows a side view of a first example of a harpoon breaching tool, according to the present invention. Harpoon  10  can comprise an elongated support shaft  12  with a front end  97  and a back end  99 , and a centerline along the length of the shaft. Shaft  12  can have a thru-hole  41 , and a loop  43  for attaching a chain to. Pivot blade  18  is pivotally mounted to the support shaft  12  by pivot/hinge pin  16 . Blade  18  has a tapered tip  26 , which can have a sharp point or a blunt point. Sliding collar  14  holds the blade  18  in a un-released position (i.e., substantially parallel to the long axis of shaft  12 ), until such time as the collar  14  slides backwards towards rear end  99 , and releases the blade  18 , which can then rotate/pivot into a locking/hooking position (e.g., perpendicular to the centerline of shaft  12 ), through an longitudinal opening (not shown) in shaft  12 . Shaft  12  can be a solid cross-section (like a bar) or a hollow cross-section (like a pipe). The cross-sectional shape of shaft  12  can be, for example, square, circular, rectangular, oval, U-shaped, T-shaped, or I-Beam shaped. It can have a round shape at one end, and a square shape at the other end. Shaft  12  can comprise multiple segments (not shown), coupled end-to-end, for extending the total length of the harpoon  10 . 
     In  FIG. 3 , pivot blade  18  serves two functions: (1) to pierce through the door or wall with the tapered tip  26 , and (2) to rotate or pivot into a “locking” or “hooking” position that hooks the door and prevents the shaft  12  from being withdrawn when pulled backwards away from the door; thereby allowing the door (or section of wall) to be rapidly pulled out of its frame. 
     Pivot/Hinge pin  16  can be selected from a wide variety of industrial pins. Industrial pins are cylindrical fasteners that are used to locate, align and join components. They are typically made out of aluminum, brass, titanium, wood and plastic. Products made from hardened steel, unhardened steel, low-carbon steel, and stainless steel are also available. There are several basic types of industrial pins. Categories include dowel pins, spring pins, cotter pins and wire clips, hitch pins and lynch pins, locating and fixture pins, and specialty products. Important dimensions for industrial pins include inner diameter, outer diameter, and length. 
     Dowel pins are industrial pins that are used to prevent motion or slippage. Straight, oversize, undersize, and knurled products are commonly available. Parallel dowel pins have ends that are machined to two different tolerances. Stepped dowel pins have two different body diameters altogether. Pull dowel pins have a threaded hole in one end so that a screw can be inserted to help remove the pin from a blind hole. Threaded and non-threaded taper pins are also available. Standard groove pins contain longitudinal grooves. By contrast, spiral groove pins contain latitudinal grooves. Escutcheon pins have a semi-spherical head at one end and a long cone at the other. They are usually hammered in place and used for light-duty jobs. Drive pins feature an interference fit and are often used to assemble components in rotary or other moving applications. 
     Industrial pins also include several types of spring pins, cotter pins and wire clips. Coiled spring pins are hollow and made of metal. Roll pins or slotted steel springs are headless, hollow fasteners with a longitudinal slot that runs down the length of the pin. Cotter pins open out after passing through a hole. A popular type is the extended or hammerlock cotter pin; however, hairpin and circle (ring) cotter pins are also available. Twist pins feature a self-locking mechanism and can be used as replacements for standard hairpin cotters. Clinch pins are manufactured with a hump on one end and are self-securing. Industrial-quality safety pins are commonly available. 
     Industrial pins also include several types of hitch pins, lynch pins, locating pins, and fixturing pins. Hitch pins have a wire loop grip at one end. Lynch pins also have a ring-shaped loop, but snap into place. Clevis pins have a head on one end and a hole in the other. Like hitch pins and lynch pins, clevis pins are used in conjunction with cotter pins. Other types of hitch pins include toggle pins, detent pins, and wire locks. A variety of locating and fixturing pins are available. Examples include clamping pins, quick release pins, drift pins, and indexing or pop pins. L-pins and T-pins have a letter-shaped handle at one end. Round pins and diamond pins have either a small or large locating shoulder. Cone locator pins can compensate for a great deal of misalignment. Floating locating pins are used to provide precise, 1-axis location while floating in the perpendicular axis. 
     Industrial pins include many types of specialized or proprietary products. Ejector pins are small fasteners that are designed to push or eject parts or materials. Expanding diameter pins expand when a cam is actuated to provide a tight fit. Shear pins are designed to break if the fastened components move in opposite, parallel directions to their mating surfaces. Weld pins are designed to be welded in place. 
       FIG. 4A  shows a side view of the front end of a harpoon breaching tool  10 . Pivot blade  18  can be a solid cylindrical rod with a tapered tip  26 , and a thru-hole for accepting a pivot/hinge pin  16 . The taper angle of tapered tip  26  may be 5-45 degrees, depending on the hardness of the tip, the strength of the door or wall being penetrated, angle of attack, etc. Alternatively, the taper angle may be in the range of 10-30 degrees, as measured from the shaft&#39;s centerline (i.e., 20-60 degrees total included angle). Hinge pin  16  pivotally connects the blade  18  to the front end of support shaft  12 . Shaft  12  can be a hollow pipe. The location of the pivot pin  16  can be offset forwards or backwards from the center-of-gravity, e.g., towards the rear end of blade  18 , so that the eccentric mounting point causes the blade to freely rotate downwards under gravity when released. Alternatively, the hinge pin can be centered on the blade&#39;s center-of-gravity. Optionally, one or more springs can be used to forcibly rotate the blade when released. A longitudinal opening/slot (not seen in this view) is disposed in the top of pipe  12  to allow the rearward portion of blade  18  rotate outwards when released. Optionally, a short slot (not seen in this view) can be cut into the bottom of pipe  12  to allow blade  18  to fully rotate into a vertical position, perpendicular to shaft  12 , when released. 
     Sliding collar  14  can have a flange or ring  15  of a larger diameter than the collar, attached to the front end of the collar, to help insure that the collar  14  will be pushed backwards when the blade  18  penetrates through the door or wall, thereby insuring release of the blade. Collar  14  can have a small hole  17  (with a matching thru-hole in pipe  12 ), for placing a small-diameter sacrificial shear pin/dowel, made from a breakable material, such as wood or plastic, whose function is to hold the collar  14  in place in the un-released/un-deployed position (i.e., covering and holding the blade in the parallel position) before striking the door. Then, during penetration, when collar  14  first makes contact with the door or wall, the sacrificial dowel in hole  17  easily shears and breaks, thereby releasing collar  14  to freely slide backwards as the shaft  12  continues to penetrate deeper through the door. The axial length of collar  14  can be about 2-3 times as long (or more) as the diameter of support shaft  12 . This can help to prevent the collar from gouging, digging-in, catching or otherwise hanging-up on the surface of pipe  12  during penetration. This could be a problem, e.g., if the axial length of the collar  14  is much less than the diameter of shaft  12  (e.g., if the collar  14  is a ring); especially if the harpoon tool  10  impacts the door or wall at an oblique angle (i.e., not perpendicular to the door), which would load one side of collar  14  more than the other, and possibly prevent sliding. The outer diameter of flange  15  can be made smaller if hanging-up during oblique angle penetration is a problem. 
     Pivot blade  18  can have a square, rectangular, circular, oval, triangular, hexagonal, U-shaped, T-shaped, or I-beam shaped cross-sectional shape; and can have a solid or hollow cross-section. 
     Preferred materials of a harpoon breaching tool  10  are primarily low-carbon steel, but can also include aluminum alloy in places where high strength is not necessarily needed, e.g., the support shaft  12  and sliding collar  14 . Blade  18  may be made of a high-strength steel; or made of a lower strength steel with a heat-treated, hardened tip  26 . The tip  26  of blade  18  may be coated with a hard coating, e.g., titanium carbide, titanium nitride, as is typically found on drill bits. Alternatively, tip  26  can be a ceramic material or a heavy metal (such as tungsten, molybdenum, depleted uranium). The hinge pin  16  can be made of a high-strength, hardened steel. 
     In some embodiments, the mass and momentum used for breaching can come from the vehicle, not the breaching tool; hence, it may not be necessary to make the tool especially heavy or massive. For example, the support shaft can be manufactured from a lightweight fiber composite (e.g., fiberglass, carbon-fiber wrapped epoxy/resin matrix, Kevlar or Spectra aramid fiber-wrapped composite). Conversely, in other embodiments, a more massive, heavier harpoon tool (e.g., made of thick-walled, Schedule 80 pipe) may provide greater impulsive power for penetrating through a concrete block wall. 
     Some examples of dimensions of harpoon breaching tool  10  can be as follows. The shaft  12  can be from 1-4 inches in diameter (or the width of a square cross-section), and can be 6-10 feet long. If the total length of harpoon  10  is about 8 feet or less, then it can fit into the bed of a pickup truck. Hinge pin  16  can be ¼″-1″ diameter. The length of blade  18  (total length from tip  26  to back end) can be 6-36 inches, preferably about 10-20 inches long. If made from a solid, cylindrical bar stock, then blade  18  can be 1″ diameter. Shaft  12  (as well as blade  18 ) can be a 1″ square solid bar or hollow channel, a 1″×2″ rectangular solid bar or hollow channel, or a 2″ square solid bar or hollow channel (the latter of which slips nicely into the square hole (about 2⅛″ wide on the inside) of a standard 2″ trailer receiver hitch on a truck. Shaft  12  and collar  14  can be made of standard, commercially available Schedule 40 or Schedule 80 steel pipe. Shaft  12  and collar  14  can be made of standard, commercially available hollow structural members with square, rectangular, U-shaped, and I-beam shaped cross-sections. In general, the smaller the diameter or width of blade  18  and shaft  14 , the easier it is to punch a hole through the door or wall. Also, the smaller the diameter or width of blade  18  and shaft  12 , the lighter the weight. However, if blade or shaft becomes too slender (thin), one has to start worrying about buckling the blade or shaft during penetration. Also, the diameter and strength of the hinge pin  16  has to be sufficiently high so as to withstand the forces generated during use. 
       FIG. 4B  shows the blade  18  rotated into the vertical, “locking” position after having been released when the collar  14  has been slid backwards sufficiently far to clear the rear end  28  of blade  18 . In this example, the pivot pin  16  is offset from the center of gravity of blade  18 , thereby allowing the blade to rotate by gravity. When the blade has rotated into the vertical/perpendicular locking position, it “hooks” the door or wall when shaft  12  is pulled back out, thereby pulling the door or section of wall along with the shaft. 
     Optionally, pivot blade  18  can have one or more fins ( 20 ,  22 ,  24 ) attached along the long axis of the blade for allowing more efficient cutting and penetration through the door or wall being breached. The front ends of the fins can have a taper angle that matches the taper angle of the pointed tip  26  of blade  18 ; or, the angles can be different. In general, the fins are attached along the front half of the blade  18  (see, for example, bottom fin  22  and side fin  24  in  FIG. 4A ). However, the top fin,  20 , can extend all the way to the back end  28  of blade  18 . The fins can be, for example, ⅛″ steel, and can be welded (spot or continuous) or brazed to blade  18 . 
       FIG. 4C  shows a cross-section view looking at the end of pipe  12 . Blade  18  is a solid cylindrical rod centered at the centerline of pipe  12 . Four fins ( 20 ,  22 ,  24  and  24 ′) are attached to rod  18 , spaced 90 degrees apart circumferentially, with the upper and lower fins  20  and  22  being aligned vertically, and the two side fins,  24  and  24 ′, being aligned horizontally. In this example, the ends of pivot pin  16  are shown as extending past the outer diameter of pipe  12 . This could represent, for example, a bolt head or a nut on a threaded end of pin  16 . However, any part of pin  16  that extends beyond pipe  12  might catch on the door or wall during penetration (and/or withdrawal), and cause problems with penetration. To help prevent this from happening, the side fins  24  and  24 ′ can be aligned along the axis of pin  16 , and extend radially at least as far out as the exposed ends of pin  16 , and, preferably, a bit more beyond (as shown in  FIG. 4C ), so as to provide a cut/slice/tear in the door or wall that allows for easier, unimpeded passage of the exposed pin ends through the door or wall. 
     In other embodiments, blade  18  can be spring-loaded, so that it pops-open and pivots outwards when the shaft is oriented in any direction relative to gravity. In this case (spring-loaded blade) the orientation of fins  20 ,  22  and  24 ,  24 ′ would not necessarily be restricted to being “vertical” and “horizontal”. However, the side fins  24 ,  24 ′ can still be aligned along hinge pin  16  in the manner shown in  FIG. 4C  (if the ends of hinge pin  16  are exposed). Blade  18  may have any number of attached fins, from 1 to 8, or more. 
     In  FIG. 4C , sliding collar  14  can be seen, surrounding pipe  12 , and has a large diameter flange  15  attached to the collar  14 . In this embodiment, where the end of the hinge pin  16  protrude out past the outer diameter of pipe  12 , this prevents the collar  14  from accidentally sliding off of the front end of harpoon  10  (i.e., towards the tapered tip  26 ). Upper slot  34  and lower slot  36 , which are cut into pipe  12 , can be seen in  FIG. 4C . In this example, upper fin  20  and lower fin  22  do not extend radially beyond the inside diameter of sliding collar  14 , in order to allow collar  14  to hold blade  18  in the horizontal (i.e., un-deployed) position prior to penetration. Optionally, a pair of washers or bushings (not shown) may be placed onto pin  16 , on either side of blade/rod  18 , to prevent rod  18  from shifting sideways (i.e., left or right in  FIG. 4C ) during use (especially during penetration at oblique angles). Keeping the blade/rod  18  centered also helps to insure that it can freely rotate into the locking position fully penetrating the door, and not get hung-up on the inside surfaces of pipe  12 . 
     Alternatively, the ends of hinge pin  16  may be located flush with, or even recessed away from, the outer surface of support shaft  12 . Pin  16  may have a thread at one end and a countersunk socket at the other for screwing the pin into a threaded hole in pipe  12 . Other types of industrial pins presented earlier can be used for pin  16 . There are many options for holding pin  16  in position; including a pressed/hammered fit, a loose fit, soldered or brazed or glued attachment, a shrink fit, a circular clip ring, etc. 
       FIG. 5  shows a cross-section side view of the harpoon of  FIG. 3 , after penetrating door  6 . This drawing illustrates a possible situation where, after penetration, the door has tilted to some non-vertical angle, for whatever reason. 
     Since blade  18  is free to rotate about hinge pin  16  through a large a large range of angles (essentially 90 degrees), and since the blade is pulled into a position that is flat against the door when being withdrawn, then this allows for the shaft  12  to remain substantially horizontal while being pulled on during removal of the door. In this way, the embodiment of  FIG. 3A  is self-adjusting for non-vertical doors and wall sections. 
       FIG. 6A  shows a cross-section top view of another example of a harpoon tool,  10 . A monolithic block/plug  50  made of steel is welded on to the front end of pipe  12 . Block  50  has a deep slot for housing blade  18 , which rotates freely on hinge pin  16 . Block  50  has a pair of tapered, conical-shaped front end shapes,  52  and  52 ′, which provide a smooth transition from the width of blade  18  to the outer diameter of pipe  12 . A 30-degree taper angle is shown; however, this angle may be too blunt and can cause the door to buckle inwards. Hence, a shallower angle, e.g., 10-20 degrees, may do a better job of penetrating the door without buckling.  FIG. 6B  shows a schematic side view of  FIG. 6A . Blade  18  is a flat, rectangular bar with a tapered tip, and is mounted offset from its center of gravity so that it rotates downward by gravity when released. The tests that we performed used this design, with 3″ schedule  80  steel pipe for pipe  12 . The sliding collar was made of 3½″ schedule  40  steel pipe. The blade was made of 1″×3″ bar stock, with a 30 degree tapered tip. The length of the blade from the tip to hinge pin  16  was 15 inches, and the length from hinge pin to rear end of the blade was 10 inches, so that the total length of the blade was 25 inches. The hinge pin was a 1″×2.5″ long grade 8 hex bolt with 12UNF threads. The length of collar  14  was 12 inches, and a 5″ diameter threaded ring was screwed onto the front end of the collar. The bolt head and other end of hinge pin  16  was recessed below the surface of pipe  12 .  FIG. 6C  shows a cross-section view cut through the hinge pin  16 , as viewed from the end of harpoon tool  10 . 
       FIG. 9  shows a cross-section side view of another example of a harpoon tool. Tool  60  has a support shaft  62 , sliding collar  64 , hinge pin  66 , pivot blade  68 , and tapered plug  70 . Tapered plug  70  can be made of a solid steel rod, with the taper angle turned on a lathe. Plug  70  may be attached to the front end of shaft  62  by, for example, welding or by a threaded connection. Threads  72  may be pipe threads, to provide a snug fit. Pivot blade  68  can rotate freely about hinge pin  66  as it rotates outwards through upper and lower slots  63 ,  65 , which are cut into shaft  62 . Blade  68  can be eccentrically mounted, to allow the bar to rotate by gravity into a locking position. Alternatively, or additionally, blade  68  can be spring-loaded. Shaft  62  can be a pipe, a hollow square channel, or a hollow rectangular channel. The joint between plug  70  and shaft  62  can be flush with the outer surface of shaft  62 , to prevent the shaft from hanging-up. Plug  70  can be permanently mounted, or removable for replacement, or re-machining (i.e., re-grinding the tip). 
       FIG. 10  shows a cross-section side view of another example of a harpoon tool. Here, a single pivot blade  88  is deployed through a single slot  83  cut in shaft  82 . When released, blade  88  rotates outwardly 90 degrees about hinge pin  86  urged by spring  87 . Hinge pin  86  is located near the front end of slot  83 , and near the front end of blade  88 . Alternatively, if the slot  83  was located on the bottom side of shaft  82 , then blade  88  could rotate and fall by gravity alone, when released. Tapered plug/tip  85  can be made of flat, rectangular bar stock, with the taper angle made by bandsaw cutting or equiv. Plug  85  may be welded to shaft  82  at weld-joint  89 . 
       FIGS. 11A and 11B  show side views and cross-section end views of a spring-loaded, offset, two-blade harpoon tool. Here, the two pivot blades  920  and  920 ′ spring out from opposite sides of the support shaft  912 , though longitudinal openings  925  and  925 ′, respectively, after being released when the sliding collar  915  has been pushed backwards. A torsion coil spring  922  is wrapped around the hinge pin  916 , and becomes pre- (i.e., “cocked”, tensioned) when the two blades are recessed inside of the shaft  912 , and held in place by the sliding collar  914 . As shown in  FIG. 11B , the hinge pin  916  is held in place by bolts  928  and  928 ′. Locking blades  920  and  920 ′ are offset on either side of the centerline of the support shaft  912 , with each blade swinging through offset openings  925  and  925 ′ in the shaft  912 . The two ends of torsion coil spring  922  are pinned to each blade  920  and  920 ′ by press-fit pins  924  and  924 ′, respectively. The spring-loaded blades spring open without the need to rely on gravity to rotate the blades. 
       FIG. 12  shows an example of a harpoon support shaft, according to the present invention. Shaft  102  has a hollow, square cross-section with a long slot  108  cut into the upper surface  103  of shaft  102 ; and a hole  104  for holding a pivot pin (not shown). The upper slot  108  accommodates the rotation of the pivot blade (not shown) as it rotates outwards about the pivot pin when released. The width of upper slot  108  is greater than the width of a pivot blade (not shown). The front end of upper slot  108  extends through the front end  106  of shaft  102  (i.e., the slot is open at the front end, and is closed at the back end). The length, L, of upper slot  108  can be at least two-times the length of a side, W, of square channel  102  (i.e., L≧2×W). 
       FIG. 13  shows another example of a harpoon support shaft, according to the present invention. Shaft  112  has a square, hollow cross-section with a long slot  118  cut into the upper surface  113  of shaft  112 , and a hole  114  for holding a pivot pin (not shown). The upper slot  118  accommodates the rotation of the pivot blade (not shown) as it rotates outwards about the pivot pin when released. The width of upper slot  118  is greater than the width of a pivot blade. The front end of upper slot  118  does not extend through the front end  116  of shaft  112 . In other words, the upper slot  118  is closed at both ends. The length, L, of upper slot  118  can be at least 2 times the length, W, of the side of square channel  112  i.e., L≧2×W. 
       FIG. 14  shows another example of a harpoon support shaft, according to the present invention. The embodiment of  FIG. 14  is the same as in  FIG. 12 , except that a second, lower slot  125  has been cut into the lower surface  127  of square shaft  122 . The lower slot  125  allows a pivot blade (not shown) to completely pivot a full 90 degrees (i.e., into a vertical position) around the pivot pin in hole  124 . The width of lower slot  125  is greater than the width of a pivot blade (not shown). The front end of lower slot  125  extends through the front end  126  of shaft  122  (i.e., the lower slot  125  is open at the front end). The length of lower slot  125  is at least as long as needed to allow a pivot blade to completely pivot 90 degrees into a position that is perpendicular to the long axis of the support shaft  122 . 
       FIG. 15A  shows a top view of another example of a harpoon breaching tool, according to the present invention. Harpoon tool  130  comprises a solid square or rectangular bar  132 , with a tapered, pointed tip  135 , a through-slot  133 , a hinge pin  136  and a pivot blade  138 . The sliding collar is not shown. 
       FIG. 15B  shows a cross-section side view of  FIG. 15A . The longitudinal opening (slot)  133  passes completely through bar  133  from top to bottom. In this example, the location of pivot pin  136  is offset forwards from the center-of-gravity of the blade  136 , which rotates into a vertical locking position by gravity. In FIG.  15 B, blade  138  is shown in the deployed, locking position. Slot  133  can be manufactured, e.g., by an Electro-Discharge Machining (EDM) cutting process, water-jet cutting, e-beam cutting, or laser-beam cutting process. 
       FIG. 15C  shows a cross-section top view for an alternative construction for  FIG. 15A . Harpoon tool  130  can be a laminated structure, made by laminating together multiple bars and pieces of metal. Side plates  131  and  137  are joined to spacer places  141  and  139 . Gap/slot  133  is naturally formed by spacer plates  139  and  141 . Pivot hole  145  goes through both side plates  131  &amp;  137 . In  FIG. 15C , the tapered tip can have the same taper angle for both side plates  131  and  137 , and the middle spacer plate  141 , so as to provide smooth and efficient penetration through a door or wall. Lamination of the plates can be done by welding around the edges, either continuously or intermittently (by hand, or e-beam weld, laser weld, or by machine welding); by brazing or soldering the plates together; by gluing (e.g., cyanoacrylate adhesive, epoxy-based adhesive, or other glues well known in the composites fabrication industry), by riveting, by screwing together, etc. Rivets can be flush or raised head. The rivets can be steel rods that are welded at each end to a countersunk region of the outer plates  131  and  137 . 
       FIG. 15D  shows a cross-section top view for an alternative laminated construction similar to  FIG. 15C . In this example, the front butt ends (e.g.,  153 ,  153 ′) of side plates  131  and  137  are flat. A pair of weld joints  151 ,  151 ′ are made at the 90 degree intersection of the butt end  153 ,  153 ′ of the side plates and the middle (spacer) plate  141 . A large, angled weld bead  151 ,  151 ′ can provide a relatively smooth transition from the tapered tip of plate  141 , past the blunt ends  153 ,  153 ′ of side plates  131  and  137 . 
       FIG. 16A  shows a cross-section side view of another example of a harpoon breaching tool. Tool  140  comprises a solid bar  142  with a tapered tip  145 , a recessed slot  143 , a pivot pin  146 , and a pivot blade  148 . Bar  142  can have a solid square, rectangular, or circular cross-section. Pivot pin  146  is mounted near the front end of blade  148 , which rotates by gravity into a substantially-vertical locking position when released by the sliding collar (not shown). In this embodiment, recessed slot  143  does not completely go through to the other side of bar  142  (as in, for example,  FIG. 15A ). Pivot blade  148  is shown in the un-released position, disposed inside the recessed slot  143  inside of support shaft  142 . Sliding collar  147  with flange or tabs  149  is located so that the collar covers at least part of blade  148 , thereby holding blade  148  in the un-released position. 
       FIG. 16B  shows a cross-section side view of the harpoon breaching tool of  FIG. 16A , after penetrating through a metal door. Here, sliding collar  147  has been pushed backwards by door  141  as the harpoon  140  passes through the penetration made in the door by tapered tip  145 . Pivot blade  148  has been released, and rotated by gravity into a vertical position, roughly perpendicular to the harpoon&#39;s centerline. Blade  148  is also roughly parallel to the plane of the metal door or wall  141 . 
       FIG. 17A  shows a cross-section top view, A-A, of another example of a harpoon breaching tool. Tool  150  has a hollow support shaft  152 , pivot blade  158 , hinge pin  156 , and a tapered tip  155  for piercing. Tip  155  is a separate, solid, “arrowhead”-like plug, with a reduced-width shank  153  that fits snugly into the front end of hollow shaft  152 . Tip  155  can be joined to shaft  152  with a one or more industrial pins  157 , e.g., a coiled spring pin or dowel pin. If tip  155  needs replacing, then the industrial pins  157  are easily knocked out or otherwise removed.  FIG. 17B  shows a cross-section side view, B-B of the tool of  FIG. 17A .  FIG. 17C  shows a cross-section end view, C-C, of the tool of  FIG. 17A . Shaft  152  and the shank  153  of tip  155  can have a square cross-section, as in this example; or be circular, rectangular, etc (as presented earlier). 
       FIG. 18A  shows a cross-section side view of an adaptor  170  for making a transition from the support shaft  172  to a square bar  174  for inserting into a trailer hitch receiver (not shown). Adaptor  170  is a hollow channel, with a square tongue  174  welded to the channel by weld  175 . Tongue  174  has a thru-hole  176 . Tongue  174  can have a solid or hollow cross-section. The harpoon&#39;s support shaft  172  inserts into the open end of adaptor  170 , and can be temporarily or permanently attached by using a weak or strong pin through hole  178 , (or, alternatively, no pin joint at all). A first metal loop  182  is welded to the underside of shaft  172 , and a second metal loop is welded to the underside of adaptor  170 . A slack, metal chain  180  is connected between the two metal loops  182  and  184 . Means for connecting the chain  180  to loops  182  and  184  include a locking, or non-locking, steel carabiner  301 , a strong hook  303 , a clevis pin, etc. 
       FIG. 18B  shows an isometric 3-D view of a harpoon support shaft  172  mounted to a trailer hitch  194 , using adaptor  170 . In this assembly, support shaft  172  is inserted into the front, open end of adaptor  170 , and is locked in place by shear pin  186 . At the back end of adaptor  170 , welded tongue  174  is inserted into a standard trailer hitch receiver  194  (e.g., 2″ hitch), and securely attached together with an industrial pin  188 . Channel section  170  may be any of the cross-section shapes listed before, such as square, circular, rectangular, U-shaped, etc. It is not required for the channel shape of adaptor  170  to have the same shape as shaft  172 . For example, as shown in  FIG. 18B , channel  170  has a square cross-section, and shaft  172  has a circular cross-section. A slack, heavy metal chain  180  is connected between loop  182  on shaft  172  and loop  184  on adaptor  170 . Trailer receiver hitch  194  is welded to the structural frame  196  of a truck or other vehicle (not shown). Either, or both, pins  186  and  188  may be secured from falling out by, e.g., using cotter pins  190  and  192 , respectively. Pin  186  can be a shear pin made of a sacrificial, breakable material (e.g., plastic, wood, small diameter steel) and/or have a small diameter, that shears (breaks) relatively easily when the shaft  172  is pulled away from adaptor  170 . After the harpoon has penetrated and hooked the door, and the pivot blade released, the vehicle reverses direction and drives away from the door. When the released pivot blade contacts the inside of the door, the moving vehicle pulls apart shaft  172  and adaptor  170  by breaking shear pin  186 . Then, as the vehicle continues to drive away, increasing the distance between the embedded harpoon and the truck, the chain  180  eventually snaps tight, thereby applying a large impulse force (i.e. “jerk”) to the harpoon by the momentum of the moving vehicle. Adaptor tongue  174  is securely pinned with pin  188  to the vehicle&#39;s receiver hitch  194 , so that the adaptor  170  remains attached to the hitch  194  when the chain snaps tight. Optionally, slack chain  180  can be bundled or loosely coiled up underneath adaptor  170  and shaft  172  with one or more weak ties  191  (e.g., plastic cable ties), to keep the chain from dragging the chain on the ground and accidentally catching on something. 
     Alternatively, chain  180  may be tied-up underneath the trailer hitch  194  with plastic cable ties. It is not required to actually use a shear pin  186  to temporarily connect shaft  172  to adaptor  170 . Instead, the connection can simply by a slid-in, friction fit; which is sufficient keep the shaft  172  from accidentally falling out of adaptor  170  while being driven around. During penetration, the back end of shaft  172  butts up against the front end of tongue  174  and is supported. Then, after hooking the door, the shaft  172  simply pulls out of adaptor  170  and falls to the ground, when the vehicle drives backwards. Alternatively, adaptor  170  can be designed to fit snugly over the tine of a fork lift. 
     Alternatively, as shown in  FIG. 18C , the harpoon&#39;s support shaft  172  can be inserted directly into trailer receiver hitch  194  and connected by pin  188  and cotter pin retainer  177 . Shaft  172  can be a 2″ square channel (hollow or solid), which fits snugly into a standard 2″ trailer receiver hitch  194 . If a slack chain is used (not shown), then pin  188  can be a weak pin, i.e., a shear pin, designed to break at a low force. Otherwise, if a slack chain is not used, then pin  188  can be a strong (i.e., essentially unbreakable) pin. 
       FIG. 18D  shows a cross-section of a first example of a modified trailer receiver hitch. The square receiver tube  514  has been modified by welding an “end-stop” back plate  518  onto the back end of the tube with weld  520 . This prevents harpoon support shaft  512  from being pushed out the back of receiver tube  514  when the harpoon is penetrating the door, but also allows shaft  512  to be easily pulled out and detached from the hitch (since the shaft is not pinned), thereby allowing the vehicle to gain momentum prior to snapping chain  522  tight. 
       FIG. 18E  shows a cross-section of another example of a modified trailer receiver hitch. The square receiver tube  614  has been modified by drilling a second thru-hole  618  for accepting a strong pin. The second thru-hole  618  is located towards the rear end of receiver tube  614 . When a strong pin and clip is placed into the second thru-hole  618 , then this serves as an “end-stop” for preventing harpoon support shaft  612  from being pushed out the back of receiver tube  614  when the harpoon impacts and penetrates the door. But, since shaft  612  is not pinned to the hitch  614 , then this also allows shaft  612  to be easily pulled out of receiver tube  614 , and separated from the vehicle; thereby allowing the vehicle to gain momentum prior to snapping chain  622  tight. 
     Optionally, the rear end of the chain (e.g., chain  622  in  FIG. 18E ), can be attached to a conventional “tow hook” that is commonly bolted to the structural frame of a car or truck. 
       FIG. 18F  shows a cross-section of another example of a modified trailer receiver hitch. As before in  FIG. 18D , square receiver tube  414  has been modified by drilling a second thru-hole  718  for accepting a strong pin and clip. The second thru-hole  718  is located towards the rear end of receiver tube  714 . When a strong pin and clip is placed into the second thru-hole  718 , then this serves as an “end-stop” for preventing harpoon support shaft  612  from being pushed out the back of receiver tube  714  when the harpoon impacts and penetrates the door. Additionally, a weak shear pin  720  is placed in the standard pin hole  722  for a standard receiver tube. After the harpoon has penetrated and hooked the door, and then the vehicle begins to drive backwards away from the door, the weak shear pin  720  breaks, thereby allowing shaft  712  to be easily pulled out of receiver tube  714  and separated from the vehicle; thereby allowing the vehicle to gain some momentum prior to snapping the chain  726  tight. Note that in this example, chain  726  is attached to a clevis pin  724  attached to a hole  725  in shaft  712 ; and chain  726  is also hooked onto hook  728  (which is attached to the frame of the vehicle). 
       FIG. 18G  shows a cross-section of another embodiment of a harpoon mounted to a trailer hitch. Support shaft  812  is inserted into trailer receiver tube  814 , and optionally pinned with a weak, shear pin  825 . A slack chain  822  can be hung between the shaft  812  and hitch  814 . Hitch  814  is welded to the truck&#39;s structural frame  816 . A one-way “stopper” member(s)  818  is welded with weld  819  to shaft  812 . Stopper  818  may be one, two, three, or four, short bars of metal, e.g., ½″×½″×2″. Alternatively, in place of stopper  818 , a hole can be drilled in shaft  812  and a large diameter bolt  827  and nut can be installed to serve as a one-way stopper. The purpose of stopper  818  (or 827) is to rigidly hold shaft  812  while penetrating the door or wall, while not interfering with the detachment of shaft  812  from receiver tube  814  when the truck drives away from the door or wall (after penetration and hooking). 
       FIG. 19  shows an elevation view of an adjustable-height triangular adaptor bracket. Bracket  210  can optionally used to mount the harpoon&#39;s support shaft  212  about 2-4 feet high off then ground, so that the harpoon&#39;s tip can impact and penetrate the door or wall at roughly mid-height (instead of penetrating the door at a height of only about 1-2 foot. Bracket  210  can be made in a wide variety of ways. For example, bracket  210  can comprise two channels  213  and  214  welded at right angle, with an angled (e.g., 45 degrees) channel  215  welded to make a rigid triangular frame. Channels  213  and  214  can be 2″ hollow, square channel. Channel  213  fits into trailer receiver hitch  220 , and is rigidly pinned through holes  217  and  222 . Hitch  220  is welded to structural frame  224 . Channel  215  can be a T or U-shaped structural channel. Bracket  210  also comprises a hollow channel  216  with a through hole  226 . Channel  216  is welded to an adjustment stem  232 , which is locked into place inside of hollow channel  214  with an industrial pin and clip. The vertical height of channel  216 /stem  232  may be adjusted up or down through a series of vertically-stacked holes  230 . Alternatively, channel  216  may be welded directly to the top of channel  214  (in which case, an adjustment stem  232  would not be needed). The rear end of support shaft  212  is mounted inside of hollow channel  216 , and is pinned together through holes  208  and  226 . The pin holding together shaft  212  and channel  216  may be weak (i.e., a shear pin), or strong (unbreakable). If a weak shear pin is used, a bundled-up, slack chain (not shown) may be attached to loop  234  on shaft  212  and to loop  236  on bracket  210 . 
     The support shaft,  132  or  142 , shown in any of  FIGS. 15A &amp; 15B  or  16 A &amp;  16 B, may comprise a bar or rod of solid metal (i.e., having a solid cross section). In these embodiments, the tapered tip ( 135  or  145 , respectively) may be an integral part of the solid shaft  132  or  142 . In other words, the tapered tip is made from the solid shaft, e.g., by grinding or turning a taper onto the blunt end of the solid bar or rod. 
     Another embodiment of the present invention is harpoon breaching kit. For example, a kit may comprise the following parts:
         a harpoon breaching tool, any one as described earlier;   a flexible connecting member, having a front end and a back end;   means for connecting the rear end of the harpoon&#39;s support shaft to the front end of the flexible connecting member;   means for connecting the rear end of the flexible connecting member to the structural frame of a vehicle, and   means for temporarily connecting the rear end of the harpoon&#39;s support shaft to the vehicle&#39;s structural frame.       

     The flexible connecting member may be a metal chain, a towing strap, or a steel cable. The means for connecting the rear end of the harpoon&#39;s support shaft to the front end of the flexible connecting member, and the means for connecting the rear end of the flexible connecting member to the structural frame of a vehicle including a locking or non-locking steel carabiner, a strong hook, clevis pin, etc. The means for temporarily connecting the rear end of the harpoon&#39;s support shaft to the vehicle&#39;s structural frame can comprise a weak, breakable, shear pin; and also can comprise a slip-on, one-way friction fit that holds the harpoon rigidly when the vehicle is driving towards the door and while penetrating the door, but allows the harpoon to be detached from the vehicle when pulled backwards away from the vehicle. 
     Test Results 
     We performed full-scale, realistic breaching tests, using the harpoon design of  FIGS. 6A ,  6 B and  6 C. We used 3″ schedule  80  steel pipe for pipe  12 . The sliding collar was made of 3½″ schedule  40  steel pipe. The blade was made of 1″×3″ bar stock, with a 30 degree tapered tip. The length of the blade from the tip to hinge pin  16  was 15 inches, and the length from hinge pin to rear end of the blade was 10 inches, so that the total length of the blade was 25 inches. The hinge pin was a 1″×2.5″ long grade 8 hex bolt with 12UNF threads. The length of collar  14  was 12 inches, and a 5″ diameter threaded ring was screwed onto the front end of the collar. The bolt head and other end of hinge pin  16  was recessed below the surface of pipe  12 . 
       FIG. 7A  shows a picture of the prototype harpoon, mounted on a trailer hitch of a truck, in the un-released position.  FIGS. 7B ,  8 A and  8 B show the same harpoon as  FIG. 7 , after the collar has slid backwards and the blade released to rotate into a locking position(s). Using this design of a vehicle-mounted harpoon tool, we tested and breached eight doors using the vehicle-assisted method of the present invention. Three were single doors. Five were doubles doors. The doors were part of two types of buildings slated to be demolished: a concrete block building and a wood-frame stud, sheet-metal building. For these tests, the harpoon was attached to a forklift and aimed at the center of the door (except for the last test where it was attached to the receiver hitch of a truck). Timing started when the forklift was approximately 20 feet from the door. The forklift moved forward and pierced the door. After the harpoon penetrated the door sufficiently, it was reversed, and the door was pulled from its hinges. Table 1 summarizes the timed data for these tests. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Timed data for breaching metal personnel doors with a harpoon in 
               
               
                 two types of buildings. 
               
             
          
           
               
                   
                   
                 Wood Frame, Sheet Metal 
                   
               
               
                   
                 Concrete Block Building 
                 Building 
                   
               
             
          
           
               
                   
                 Single 
                 Double 
                 Double 
                 Double 
                 Double 
                 Single 
                 Single 
                 Single 
                 Average 
               
               
                 Event 
                 sec. 
                 sec. 
                 sec. 
                 sec. 
                 sec. 
                 sec. 
                 sec. 
                 sec. 
                 sec. 
               
               
                   
               
             
          
           
               
                 Start test 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
               
               
                 Harpoon contacts door. 
                 4 
                 4 
                 3 
                 4 
                 3 
                 2 
                 2 
                 2 
                 3 
               
               
                 Push harpoon through 
                 5 
                 6 
                 12 
                 4 
                 4 
                 3 
                 2 
                 4 
                 5 
               
               
                 Door forced open 
                 9 
                 10 
                 18 
                 13 
                 5 
                 4 
                 4 
                 N/A 5   
                 9 
               
               
                 Door freed from hinges or harpoon pulled back 
                 10 
                 11 1,2   
                 20 
                 20 1,4   
                 10 1,3   
                 9 1,4   
                 9 1,3,4   
                 7 1,5,6   
                 12 
               
               
                   
               
               
                 Notes: 
               
               
                   1 Harpoon blade did not release. 
               
               
                   2 Door did not come off hinges. 
               
               
                   3 Door frame detaches from wall. 
               
               
                   4 Doors dangles from frame. 
               
               
                   5 Door did not open. 
               
               
                   6 Test conducted with truck. 
               
             
          
         
       
     
     As can be seen from the data, breaching with a harpoon was quick, averaging just 9 seconds to force the door opened. In all but one test, the door was successfully forced opened. In six of the tests, the blade of the harpoon did not release, preventing it from locking on the inside of the door. This can be attributed to the fact that shaft of the harpoon at the hinge point flares out. This causes the door to be pushed in, instead of allowing the harpoon shaft to penetrate further, pushing the collar away to release the blade. 
     When two of the doors were breached in the wood-frame building, the frame was torn from the wood-studded wall. Wood-stud walls generally cannot withstand a significant force to the doorframe, such as that experienced in these tests. The concrete block building supported the doorframes much better. 
     In the test where the harpoon was mounted to the truck, the harpoon blade did not penetrate far enough to release. The door creased half way up the door. When truck reversed direction, the harpoon simply slid out of the hole. This can be attributed to the weak doorframe and the blunt flare on the shaft of the harpoon. 
     An improvement to the harpoon design would be to reduce the diameter of the shaft from 3 inches to 1½ inches and add fins just after the tip of the harpoon. The fins will help cut the door skin to allow the 1½ inch pipe to penetrate the door surface and not hang up at the hinge point. Instead of using a 3-inch-wide blade, a small 1-inch-diameter rod with a sharpened tip will penetrate the door skin easier. It can be constructed from standard materials such piping, bar stock, and plate steel. A variation in the design would allow the several sections of the shaft to be added to extend the reach. Also, the device can be made such that the angle of the shaft relative to the hitch can be adjusted enabling the harpoon to be centered on the door. 
     The particular examples discussed above are cited to illustrate particular embodiments of the invention. Other applications and embodiments of the apparatus and method of the present invention will become evident to those skilled in the art. It is to be understood that the invention is not limited in its application to the details of construction, materials used, and the arrangements of components set forth in the following description or illustrated in the drawings. 
     The scope of the invention is defined by the claims appended hereto.