Bombsight A bombsight is a device used by aircraft to accurately drop bomb s . Bombsights are a feature of most aircraft from World War I on , first found on the purpose - designed bomber aircraft , and then moving to fighter - bomber s and modern tactical aircraft as these aircraft took up the brunt of the bombing role . A bombsight has to estimate the path the bomb will take after release from the aircraft . The two primary forces during its fall are gravity and air drag , which make the path of the bomb through the air roughly parabolic . There are additional factors such as changes in air density and wind that may be considered , but these are only a concern for bombs that spend a significant portion of a minute falling through the air . These effects can be minimized by reducing the fall time though low - level bombing or by increasing the speed of the bombs . These effects are combined in the dive bomber . However , low - level bombing also increases the danger to the bomber from ground - based defences , and accurate bombing from higher altitudes has always been desired . This has led to a series of increasingly sophisticated bombsight designs dedicated to high - altitude level bombing . Since their first application prior to WWI , bombsights have gone though several major revisions . The earliest systems were iron sights that were pre - set to an estimated fall angle . In some cases these consisted of nothing more than a series of nails hammered into a convenient spar , lines drawn on the aircraft , or visual alignments of certain parts of the structure . These were replaced by the earliest custom - designed systems , normally iron sights that could be set based on the aircraft ' s airspeed and altitude . These early systems were replaced by the vector bombsights , which added the ability to measure and adjust for winds . Vector bombsights were useful for altitudes up to about 3 , 000 m and speeds up to about 300 km / h . Starting in the 1930s , mechanical computer s with the performance needed to " solve " the equations of motion were incorporated into the new tachometric bombsights , the most famous being the Norden . Later in World War II , tachometric bombsights were often combined with radar systems to allow accurate bombing through clouds or at night . When post - war studies demonstrated that bomb accuracy was roughly equal when optically or radar guided , optical bombsights were generally removed and the role passed to dedicated radar bombsights . Finally , especially from the 1960s on , fully computerized bombsights were introduced , which combined the bombing with long - range navigation and mapping . Modern aircraft do not have a bombsight , " per se " , instead using highly computerized systems that combine bombing , gunnery , missile fire and navigation into a single heads up display . These systems have the performance to calculate the bomb trajectory in real time as the aircraft manoeuvres , and add the ability to adjust for weather , relative altitude , relative speeds for moving targets , and climb or dive angle . This makes them useful both for level bombing , as in earlier generations , and tactical missions formerly bombed by eye . Bombsight concepts . Forces on a bomb . It is a basic outcome of Newtonian mechanics that vertical and horizontal motion of a bomb can be considered separately . This makes understanding the motion of a bomb through the air much simpler . There are some effects that operate along the changing path of the bomb , but they are relatively minor and can be considered separately for a basic study . To start with , consider only the vertical motion of a bomb . In this direction the bomb will be subject to two primary forces , gravity and drag , the first constant , and the second varying with the square of velocity . In the first instant after release the vertical motion is zero for an aircraft flying straight and level . In this case , the drag is zero , and the bomb accelerates downward due to gravity . As its velocity increases , so too does the drag force . At some point the force of drag will become equal to the force of gravity , and the bomb will reach terminal velocity . As the air drag will also vary with air density , and thus altitude , the terminal velocity will vary as the bomb falls . Generally the bomb will slow as it reaches lower altitudes where the air is denser , but the relationship is complex . Now consider the horizontal motion . At the instant it leaves the shackles , the bomb carries the forward speed of the aircraft with it . This motion is countered solely by drag , which starts to slow the forward motion . As the forward motion slows , the drag force drops and the deceleration diminishes . The forward speed is never entirely bled off . If the bomb was not subject to drag , its path would be purely ballistic and it would impact at an easily calculable point , the " vacuum range " . In practice , the impact point is short of the vacuum range , and this real - world distance between dropping and impact is known simply as the " range " . The difference between the vacuum range and actual range is known as the " trail " , as the bomb appears to trail behind the aircraft as it falls . The trail and range differ for different bombs due to their individual aerodynamics , and typically have to be measured on a bombing range . The main problem in completely separating the motion into vertical and horizontal components is the terminal velocity . Bombs are designed to fly with the nose pointed forward into the relative wind , typically through the use of fins at the back of the bomb . It is primarily the wind acting on the nose that causes drag , so the velocity that defines the drag is a factor of the angle of attack of the bomb at any given instant . If the bomb is released at low speeds , it will quickly turn vertical and the velocity will be defined largely by how long the bomb has been falling . However , if it is released at high speed , it may already be close to terminal velocity and can only accelerate vertically after bleeding off some of its horizontal speed . Reaching terminal velocity tends to " flatten " the trajectory , keeping the bomb in the air longer , and thereby allowing the horizontal speed to act over a longer time , extending the range . Finally , consider the effects of wind . Wind acts on the bomb through drag , and is thus a function of the wind speed . This is typically only a fraction of the speed of the bomber or the terminal velocity , so it only becomes a factor at very high altitudes where this small force has enough time to build up to a measurable value . However , as the bomber itself is also effected by the wind ; the bomb will leave the aircraft with both the forward airspeed of the bomber , as well as any additional motion due to the wind . This velocity is added to the velocity of the aircraft , and may represent a fairly significant adjustment . The difference between the impact point and where it would have fallen if there had been no wind is known as " drift " , or " cross trail " . The " bombsight problem " . In ballistics terms , it is traditional to talk of the calculation of aiming of ordnance as the " solution " . The " bombsight problem " is the calculation of the location in space where the bombs should be dropped in order to hit the target when all of the effects noted above are taken into account . In the absence of wind , the bombsight problem is fairly simple . The impact point is a function of three factors , the aircraft ' s altitude , its forward speed , and the terminal velocity of the bomb . In many early bombsights , the first two inputs were adjusted by separately setting the front and back sights of an iron sight , one for the altitude and the other for the speed . Terminal velocity , which extends the fall time , can be accounted for by raising the effective altitude by an amount that is based on the bomb ' s measured ballistics . When windage is accounted for , the calculations become more complex . As the wind can operate in any direction , bombsights generally re - calculate the windage by converting it into the portions that act along the flight path and across it . In practice , it was generally simpler to have the aircraft fly in such a way to zero out any sideways motion before the drop , and thereby eliminate this factor . This is normally accomplished using a common flying techniques known as " crabbing " or sideslip . Bombsights are sighting devices that are pointed in a particular direction , or " aimed " . Although the solution outlined above returns a point in space , simple trigonometry can be used to convert this point into an angle relative to the ground . The bombsight is then set to indicate that angle . The bombs are dropped when the target passes through the sights . The distance between the aircraft and target at that moment is the " range " , so this angle is often referred to as the " range angle " , although " dropping angle " , " aiming angle " , " bombing angle " and similar terms are often used as well . In practice , some or all of these calculations are carried out using angles and not points in space , skipping the final conversion . Accuracy . The accuracy of the drop is affected both by inherent problems like the randomness of the atmosphere or bomb manufacture , as well as more practical problems like how close to flat and level the aircraft is flying or the accuracy of its instruments . This inaccuracies compound over time , so increasing the altitude of the bomb run , thereby increasing the fall time , has a significant impact on the final accuracy of the drop . It is useful to consider a single example of a bomb being dropped on a typical mission . In this case we will consider the AN - M65 500 lbs General Purpose Bomb , widely used by the USAAF and RAF during WWII , with direct counterparts in the armouries of most forces involved . Ballistic data on this bomb can be found in " Terminal Ballistic Data , Volume 1 : Bombing " . Against men standing in the open , the 500 lbs has a lethal radius of about 350 feet , but much less than that against buildings , perhaps 90 feet . The M65 will be dropped from a Boeing B - 17 flying at 200 mph at an altitude of 20 , 000 feet in a 25 mph wind . Given these conditions , the M65 would travel approximately 6 , 500 feet forward before impact , for a trail of about 1000 feet from the vacuum range , and impact with a velocity of 1150 fps at an angle of about 77 degrees from horizontal . A 25 mph wind would be expected to move the bomb about 300 feet during that time . The time to fall is about 37 seconds . Assuming errors of 5 % in every major measurement , we can estimate those effects on accuracy based on the methodology and tables in the guide . A 5 % error in altitude at 20 , 000 feet would be 1 , 000 feet , so the aircraft might be anywhere from 19 to 21 , 000 feet . According to the table , this would result in an error around 10 to 15 feet . A 5 % error in airspeed , 10 mph , would cause an error of about 15 to 20 feet . In terms of drop timing , errors on the order of one - tenth of a second are reasonable . In this case the error is simply the ground speed of the aircraft over this time , or about 30 feet . All of these are well within the lethal radius of the bomb . The wind affects the accuracy of the bomb in two ways , pushing directly on the bomb while it falls , as well as changing the ground speed of the aircraft before the drop . In the case of the direct effects on the bomb , a measurement that has a 5 % error , 1 . 25 mph , that would cause a 5 % error in the drift , which would be 17 . 5 feet . However , that 1 . 25 mph error , or 1 . 8 fps , would also be added to the aircraft ' s velocity . Over the time of the fall , 37 seconds , that would result in an error of 68 feet , which is at the outside limit of the bomb ' s performance . The " measurement " of the wind speed is a more serious concern . Early navigation systems generally measured it using a dead reckoning procedure that compares measured movement over the ground with the calculated movement using the aircraft instruments . The Federal Aviation Administration ' s FAR Part 63 suggests 5 to 10 % accuracy of these calculations , the US Air Force ' s AFM 51 - 40 gives 10 % , and the US Navy ' s H . O . 216 at a fixed 20 miles or greater . Compounding this inaccuracy is the fact that it is made using the instrument ' s airspeed indication , and as the airspeed in this example is about 10 times that of the wind speed , its 5 % error can led to great inaccuracies in wind speed calculations . Eliminating this error through the direct measurement of ground speed ( instead of calculating it ) was a major advance in the " tachometric " bombsights of the 1930s and 40s . Finally , consider errors of the same 5 % in the equipment itself , that is , an error of 5 % in the setting of the range angle , or a similar 5 % error in the levelling of the aircraft or bombsight . For simplicity , consider that 5 % to be a 5 degree angle . Using simple trigonometry , 5 degrees at 20 , 000 feet is approximately 1 , 750 feet , an error that would place the bombs far outside their lethal radius . In tests , accuracies of 3 to 4 degrees were considered standard , and angles as high as 15 degrees were not uncommon . Given the seriousness of the problem , systems for automatic levelling of bombsights was a major area of study before WWII , especially in the US . Early systems . All of the calculations needed to predict the path of a bomb can be carried out by hand , with the aid of calculated tables of the bomb ballistics . However , the time to carry out these calculations is not trivial . Using visual sighting , the range at which the target is first sighted remains fixed , based on eyesight . As aircraft speeds increase , there is less time available after the initial spotting to carry out the calculations and correct the aircraft ' s flight path to bring it over the proper drop point . During the early stages of bombsight development , the problem was addressed by reducing the allowable engagement envelope , thereby reducing the need to calculate marginal effects . For instance , when dropped from very low altitudes , the effects of drag and wind during the fall will be so small that they can be ignored . In this case only the forward speed and altitude have any measurable effect . One of the earliest recorded examples of such a bombsight was built in 1911 by Lieutenant Riley E . Scott , of the U . S . Army Coast Artillery Corps . This was a simple device with inputs for airspeed and altitude which was hand - held while lying prone on the wing of the aircraft . After considerable testing , he was able to build a table of settings to use with these inputs . In testing at College Park , Maryland , Scott was able to place two 18 pound bombs within 10 feet of a 4 - by - 5 foot target from a height of 400 feet . In January 1912 , Scott won $ 5 , 000 for first place in the Michelin bombing competition at Villacoublay Airdrome in France , scoring 12 hits on a 125 - by - 375 foot target with 15 bombs dropped from 800 meters . In spite of early examples like Scott ' s prior to the war , during the opening stages of the First World War bombing was almost always carried out by eye , dropping the small bombs by hand when the conditions looked right . As the use and roles for aircraft increased during the war , the need for better accuracy became pressing . At first this was accomplished by sighting off parts of the aircraft , such as struts and engine cylinders , or drawing lines on the side of the aircraft after test drops on a bombing range . These were useful for low altitudes and stationary targets , but as the nature of the air war expanded , the needs quickly outgrew these solutions as well . One of the earliest fully developed bombsights to see combat was the German Görtz bombsight , developed for the Gotha heavy bombers . The Görtz used a telescope with a rotating prism at the bottom which was pre - set to an angle read from a table of speed and altitude . The bombardier would rotate the prism to keep the target in view , while using a spirit level to keep the instrument level with the ground . Similar bombsights were developed in France and England , notably the Michelin and Central Flying School Number Seven bombsight . All of these shared the problem that they had no way to account for windage across the aircraft ' s path , and required the aircraft to fly directly along the wind line in order to be accurate . Even then , the adjustment for drift in setting the trail was normally estimated using a stopwatch and manually timing the flight of the aircraft over the ground , a time - consuming and error - prone process . The first successful attack on the windage problem was made by Harry Wimperis , better known for his later role in the development of radar in England . In 1916 he introduced the Drift Sight , which added a simple system for directly measuring the wind speed . The bomb aimer would first dial in the altitude and airspeed of the aircraft . Doing so rotated a metal bar on the right side of the bombsight . Prior to the bomb run , the bomber would fly at right angles to the bomb line , and the bomb aimer would look past the rod to watch the motion of objects on the ground . He would then adjust the wind speed setting until the motion was directly along the rod . This action measured the wind speed , and moved the sights to the proper angle to account for it , eliminating the need for separate calculations . A later modification was added to calculate the difference between true and indicated airspeed , which grows with altitude . This version was the Drift Sight Mk . 1A , introduced on the Handley Page O / 400 heavy bomber . Variations on the design were common , like the US Estoppey bombsight . All of these bombsights shared the problem that they were unable to deal with wind in any direction other than along the path of travel . That made them effectively useless against moving targets , like submarine s and ships . Unless the target just happened to be travelling directly in line with the wind , their motion would carry the bomber away from the wind line as they approached . Additionally , as anti - aircraft artillery grew more effective , they would often pre - sight their guns along the wind line of the targets they were protecting , knowing that attacks would come from those directions . A solution for attacking cross - wind was sorely needed . Vector bombsights . Calculating the effects of an arbitrary wind on the path of an aircraft was already a well - understood problem in air navigation , one requiring basic vector mathematics . Wimperis was very familiar with these techniques , and would go on to write a seminal introductory text on the topic . The same calculations would work just as well for bomb trajectories , with some minor adjustments to account for the changing velocities as the bombs fell . Even as the Drift Sight was being introduced , Wimperis was working on a new bombsight that helped solve these calculations and allow the effects of wind to be considered no matter the direction of the wind or the bomb run . The result was the Course Setting Bomb Sight ( CSBS ) , called " the most important bomb sight of the war " . Dialling in the values for altitude , airspeed and the speed and direction of the wind rotated and slid various mechanical devices that solved the vector problem . Once set up , the bomb aimer would watch objects on the ground and compare their path to thin wires on either side of the sight . If there was any sideways motion , the pilot could slip - turn to a new heading in an effort to cancel out the drift . A few attempts were typically all that was needed , at which point the aircraft was flying in the right direction to take it directly over the drop point , with zero sideways velocity . The bomb aimer ( or pilot in some aircraft ) then sighted through the attached iron sights to time the drop . The CSBS was introduced into service in 1917 and quickly replaced earlier sights on aircraft that had enough room - the CSBS was fairly large . Versions for different speeds , altitudes and bomb types were introduced as the war progressed . After the war , the CSBS continued to be the main bombsight in British use , thousands were sold to foreign air forces , and numerous versions were created for production around the world . A number of experimental devices based on a variation of the CSBS were also used , notably the US ' s Estoppey D - 1 sight , developed shortly after the war , and similar versions from many other nations . These " vector bombsights " all shared the basic vector calculator system and drift wires , differing primarily in form and optics . As bombers grew and multi - place aircraft became common , it was no longer possible for the pilot and bombardier to share the same instrument , and hand signals were no longer visible if the bombardier was below the pilot in the nose . A variety of solutions using dual optics or similar systems were suggested in the post - war era , but none of these became widely used . This led to the introduction of the " pilot direction indicator " , an electrically - driven pointer which the bomb aimer used to indicate corrections from a remote location in the aircraft . Vector bombsights remained the standard by most forces well into the Second World War , and was the main sight in British service until 1942 . This was in spite of the introduction of newer sighting systems with great advantages over the CSBS , and even newer versions of the CSBS that failed to be used for a variety of reasons . The later versions of the CSBS , eventually reaching the Mark X , included adjustments for different bombs , ways to attack moving targets , systems for more easily measuring winds , and a host of other options . Tachometric bombsights . One of the main problems using vector bombsights was the long straight run needed before dropping the bombs . This was needed so the pilot would have enough time to accurately account for the effects of wind , and get the proper flight angle set up with some level of accuracy . If anything changed during the bomb run , especially if the aircraft had to maneuver in order to avoid defences , everything had to be set up again . Additionally , the introduction of monoplane bombers made the adjustment of the angles more difficult , because they were not able to slip - turn as easily as their earlier biplane counterparts . They suffered from an effect known as " Dutch roll " that made the more difficult to turn and tended to " hunt " after levelling . This further reduced the time the bomb aimer had to adjust the path . One solution to this later problem had already been used for some time , the use of some sort of gimbal system to keep the bombsight pointed roughly downward during maneuvering or being blown around by wind gusts . Experiments as early as the 1920s had demonstrated that this could roughly double the accuracy of bombing . The US carried out an active program in this area , including Estoppey sights mounted to weighted gimbal s and Sperry Gyroscope ' s experiments with US versions of the CSBS mounted to what would today be called an inertial platform . These same developments led to the introduction of the first really useful autopilots , which could be used to directly dial in the required path and have the aircraft fly to that heading with no further input . A variety of bombing systems using one or both of these systems were considered throughout the 1920s and 30s . During the same period , a separate line of development was leading to the first reliable mechanical computer s . These could be used to replace a complex table of numbers with a carefully shaped cam - like device , and the manual calculation though a series of gears or slip wheels . Originally limited to fairly simple calculations consisting of additions and subtractions , by the 1930s they had progressed to the point where they were being used to solve differential equations . For bombsight use , such a calculator would allow the bomb aimer to dial in the basic aircraft parameters - speed , altitude , direction , and known atmospheric conditions - and the bomb sight would automatically calculate the proper aim point in a few moments . Some of the traditional inputs , like airspeed and altitude , could even be taken directly from the aircraft instruments , eliminating operational errors . Although these developments were well known within the industry , only the US Army Air Corps and US Navy put any concerted effort into development . During the 1920s , the Navy funded development of the Norden bombsight while the Army funded development of the Sperry O - 1 . Both systems were generally similar ; a bomb sight consisting of a small telescope was mounted on a stabilizing platform to keep the sighting head stable . A separate mechanical computer was used to calculate the aim point . The aim point was fed back to the sight , which automatically rotated the telescope to the correct angle to account for drift and aircraft movement , keeping the target still in the view . When the bomb aimer sighted through the telescope , he could see any residual drift and relay this to the pilot , or later , feed that information directly into the autopilot . Simply moving the telescope to keep the target in view had the side effect of fine - tuning the windage calculations continuously , and thereby greatly increasing their accuracy . For a variety of reasons , the Army dropped their interest in the Sperry , and features from the Sperry and Norden bombsights were folded into new models of the Norden . The Norden then equipped almost all US high - level bombers , most notably the B - 17 Flying Fortress . In tests , these bombsights were able to generate fantastic accuracy . In practice , however , operational factors seriously upset them , to the point that pinpoint bombing using the Norden was eventually abandoned . Although the US put the most effort into development of the tachometric concept , they were also being studied elsewhere . In the UK , work on the Automatic Bomb Sight ( ABS ) had been carried on since the mid - 30s in an effort to replace the CSBS . However , the ABS did not include stabilization of the sighting system , nor the Norden ' s autopilot system . In testing the ABS proved to be too difficult to use , requiring long bomb runs to allow the computer to " solve " the aim point . When RAF Bomber Command complained that even the CSBS had too long a run - in to the target , efforts to replace it with the ABS ended . For their needs they developed a new vector bombsight , the Mk . XIV . The Mk . XIV featured a stabilizing platform and aiming computer , but worked more like the CSBS in overall functionality - the bomb aimer would set the computer to move the sighting system to the proper angle , but the bombsight did not " track " the target or attempt to correct the aircraft path . The advantage of this system was that it was dramatically faster to use , and could be used even while the aircraft was manoeuvring , only a few seconds of straight - line flying were needed . Facing a lack of production capability , Sperry was contracted to produce the Mk . XIV in the US , calling it the Sperry T - 1 . Both the British and Germans would later introduce Norden - like sights of their own . Based at least partially on information about the Norden passed to them through the Duquesne Spy Ring , the Luftwaffe developed the Lotfernrohr 7 . The basic mechanism was almost identical to the Norden , but much smaller . In certain applications the Lotfernrohr 7 could be used by a single - crew aircraft , as was the case for the Arado Ar 234 , the world ' s first operational jet bomber . Late in the war the RAF had the need for accurate high - altitude bombing and introduced a stabilized version of the earlier ABS , the hand - built Stabilized Automatic Bomb Sight ( SABS ) . It was produced in such limited numbers that it was at first used only by the famed No . 617 Squadron RAF , The Dambusters . All of these designs collectively became known as " tachometric sights " , " tachometric " referring to the timing mechanisms which counted the rotations of a screw or gear that ran at a specified speed . Radar bombing and integrated systems . In the pre - World War II era there had been a long debate about the relative merits of daylight versus night - time bombing . At night the bomber is virtually invulnerable ( until the introduction of radar ) but finding its target was a major problem . In practice , only large targets such as cities could be attacked . During the day the bomber could use its bombsights to attack point targets , but only at the risk of being attacked by enemy fighter s and anti - aircraft artillery . During the early 1930s the debate had been won by the night - bombing supporters , and the RAF and Luftwaffe started construction of large fleets of aircraft dedicated to the night mission . As " the bomber will always get through " , these forces were strategic in nature , largely a deterrent to the other force ' s own bombers . However , new engines introduced in the mid - 1930s led to much larger bombers that were able to carry greatly improved defensive suites , while their higher operational altitudes and speeds would render them less vulnerable to the defences on the ground . Policy once again changed in favour of daylight attacks against military targets and factories , abandoning what was considered a cowardly and defeatist night - bombing policy . In spite of this change , the Luftwaffe continued to put some effort into solving the problem of accurate navigation at night . This led to the Battle of the Beams during the opening stages of the war . The RAF returned in force in early 1942 with similar systems of their own , and from that point on , radio navigation systems of increasing accuracy allowed bombing in any weather or operational conditions . The Oboe system , first used operationally in early 1943 , offered real - world accuracies on the order of 35 yards , much better than any optical bombsight . The introduction of the British H2S radar further improved the bomber ' s abilities , allowing direct attack of targets without the need of remote radio transmitters , which had range limited to the line - of - sight . By 1943 these techniques were in widespread use by both the RAF and USAAF , leading to the H2X and then a series of improved versions like the AN / APQ - 13 and AN / APQ - 7 used on the Boeing B - 29 Superfortress . These early systems operated independently of any existing optical bombsight , but this presented the problem of having to separately calculate the trajectory of the bomb . In the case of Oboe , these calculations were carried out before the mission at the ground bases . But as daylight visual bombing was still widely used , conversions and adaptations were quickly made to repeat the radar signal in the existing bombsights , allowing the bombsight calculator to solve the radar bombing problem . For instance , the AN / APA - 47 was used to combine the output from the AN / APQ - 7 with the Norden , allowing the bomb aimer to easily check both images to compare the aim point . Analysis of the results of bombing attacks carried out using radio navigation or radar techniques demonstrated accuracy was essentially equal for the two systems - night time attacks with Oboe were able to hit targets that the Norden could not during the day . With the exception of operational considerations - limited resolution of the radar and limited range of the navigation systems - the need for visual bombsights quickly disappeared . Designs of the late - war era , like the Boeing B - 47 Stratojet and English Electric Canberra retained their optical systems , but these were often considered secondary to the radar and radio systems . In the case of the Canberra , the optical system only existed due to delays in the radar system becoming available . Postwar developments . The strategic bombing role was following an evolution over time to ever - higher , ever - faster , ever - longer - ranged missions with ever - more - powerful weapons . Although the tachometric bombsights provided most of the features needed for accurate bombing , they were complex , slow , and limited to straight - line and level attacks . In 1946 the US Army Air Force asked the Army Air Forces Scientific Advisory Group to study the problem of bombing from jet aircraft that would soon be entering service . They concluded that at speeds over 1 , 000 knots , optical systems would be useless - the visual range to the target would be less than the range of a bomb being dropped at high altitudes and speeds . At the attack ranges being considered , thousands of miles , radio navigation systems would not be able to offer both the range and the accuracy needed . This demanded radar bombing systems , but existing examples did not offer anywhere near the required performance . At the stratospheric altitudes and long " sighting " ranges being considered , the radar antenna would need to be very large to offer the required resolution , yet this ran counter for the need to develop an antenna that was as small as possible in order to reduce drag . They also pointed out that many targets would not show up directly on the radar , so the bombsight would need the ability to drop at points relative to some landmark that did appear , the so - called " offset aiming points " . Finally , the group noted that many of the functions in such a system would overlap formerly separate tools like the navigation systems . They proposed a single system that would offer mapping , navigation , autopilot and bomb aiming , thereby reducing complexity , and especially the needed space . Such a machine first emerged in the form of the AN / APQ - 24 , and later the " K - System " , the AN / APA - 59 . Through the 1950s and 1960s , radar bombing of this sort was common and the accuracy of the systems were limited to what was needed to support attacks by nuclear weapon s - a circular error probable ( CEP ) of about 3 , 000 feet was considered adequate . As mission range extended to thousands of miles , bombers started incorporating inertial guidance and star tracker s to allow accurate navigation when far from land . These systems quickly improved in accuracy , and eventually became accurate enough to handle the bomb dropping without the need for a separate bombsight . This was the case for the 1 , 500 foot accuracy demanded of the B - 70 Valkyrie . Modern systems . During the Cold War the weapon of choice was a nuclear one , and accuracy needs were limited . Development of tactical bombing systems , notably the ability to attack point targets with conventional weapons that had been the original goal of the Norden , was not considered seriously . Thus when the US entered the Vietnam War , their weapon of choice was the Douglas A - 26 Invader equipped with the Norden . Such a solution was inadequate . At the same time , the ever - increasing power levels of new jet engines led to fighter aircraft with bomb loads similar to heavy bombers of a generation earlier . This generated demand for a new generation of greatly improved bombsights that could be used by a single - crew aircraft and employed in fighter - like tactics , whether high - level , low - level , in a dive towards the target , or during hard maneuvering . A specialist capability for toss bombing also developed in order to allow aircraft to escape the blast radius of their own nuclear weapon s , something that required only middling accuracy but a very different trajectory that initially required a dedicated bombsight . As electronics improved , these systems were able to be combined together , and then eventually with systems for aiming other weapons . They may be controlled by the pilot directly and provide information through the heads - up display or a video display on the instrument panel . The definition of bombsight is becoming blurred as " smart " bombs with in - flight guidance , such as laser - guided bomb s or those using GPS replace " dumb " gravity bomb s .