The Jagdtiger ("Hunting Tiger"; officially designated Panzerjäger Tiger Ausf. B[citation needed]) is a German casemate-type heavy tank destroyer (Jagdpanzer) of World War II. It was built upon the slightly lengthened chassis of a Tiger II. Its ordnance inventory designation was Sd.Kfz. 186.
 The 72-tonne Jagdtiger was the heaviest armored fighting vehicle (AFV) used operationally by any nation in WWII and the heaviest combat vehicle of any type to be produced during the conflict. it was armed with a 12.8 cm Pak 44 L/55 main gun which could out-range and defeat any AFV fielded by the Allied forces.
 It saw brief service in small numbers from late 1944 until the end of the war on both the Western and Eastern Front. Although 150 were ordered, only around 80 were produced. Due to an excessive weight and an underpowered drivetrain system, the Jagdtiger was plagued with mobility and mechanical problems. Three Jagdtigers survive in museums.
 With the success of the StuG III, Marder I, Marder II, and Marder III Panzerjäger, the military leadership of Nazi Germany decided to use the chassis of existing armored fighting vehicles as the basis for self-propelled guns (serving as assault guns and tank destroyers). German tank destroyers of World War II used fixed casemates instead of fully rotatable turrets to significantly reduce the cost, weight, and materials necessary for mounting large-caliber guns.
 In early 1942, a request was made by the Army General Staff to mount a 128 mm gun on a self-propelled armored chassis. Firing tests of the 128 mm gun showed it to have a high percentage of hits; smaller caliber guns, such as the ubiquitous 88 mm and the slightly larger 105 mm, were also tested.
 By early 1943, a decision was made to install a 128 mm gun on either a Panther or Tiger I chassis as a heavy assault gun. The Panther chassis was considered unsuitable after a wooden mockup of the design was constructed. On 20 October 1943, another wooden mockup was constructed on a Tiger II heavy tank chassis, and presented to Hitler in East Prussia. Two prototypes were produced: One was a version fitted with the eight-roadwheel Porsche suspension system (serial number 305001) and another version was equipped with the Henschel nine-overlapping roadwheel suspension system (serial number 305002), as used on the main-production Tiger IIs constructed by Henschel. They were completed in February 1944. It was originally designated as Jagdpanzer VI but was later renamed as the Jagdtiger[citation needed] and received the Sd.Kfz. 186 designation as its inventory ordnance number.
 The Jagdtiger was a logical extension of the creation of Jagdpanzer designs from tank designs, such as the Jagdpanzer IV or the Jagdpanther from the Panzer IV and Panther tanks respectively, with a fully armored and enclosed casemate-style fighting compartment. The Jagdtiger used a boxy superstructure, with its sides integral with the hull sides, on top of a lengthened Tiger II chassis. Unlike the Jagdpanther, the Jagdtiger's casemate design did not extend its glacis plate upwards in one piece to the full height of the casemate's "roof" – it used a separate forward plate to form its casemate structure atop the hull roof, and mount its anti-tank gun. The resulting vehicle featured very heavy armor. It had 250 mm (9.8 in) armor on the front of the casemate and 150 mm (5.9 in) on the glacis plate. The main gun mount had a limited traverse of only 10 degrees; the entire vehicle had to be turned to aim outside that narrow field of fire.
 The Jagdtiger suffered from a variety of mechanical and technical problems due to its immense weight and under-powered engine. The vehicle had frequent breakdowns; ultimately more Jagdtigers were lost to mechanical problems or lack of fuel than to enemy action.
 One hundred and fifty Jagdtigers were initially ordered but only between 70 and 85 were produced at the Nibelungenwerk at St. Valentin, from July 1944 to May 1945. Eleven of them, serial numbers 305001 and 305003 to 305012, were produced with the Porsche suspension (with eight road wheels per side); all the rest used the Henschel suspension with nine road wheels per side. 
 Important parts such as the tub, superstructure and drive wheels were supplied by the Eisenwerke Oberdonau. Details and production locations were known to the Allies through the resistance group around the later executed priest Heinrich Maier. Prisoners from the St. Valentin concentration camp were used to build the tank. 
 Production figures vary depending on source and other factors such as if prototypes are included and if those made after VE day are included: approximately 48 from July 1944 to the end of December 1944; 36 from January to April 1945, serial numbers from 305001 to 305088.
 After serial number 305011 (September 1944), no Zimmerit anti-magnetic paste was factory applied.
 Only two heavy anti-tank battalions (schwere Panzerjäger-Abteilung), numbered the 512th and 653rd, were equipped with Jagdtigers, with the first vehicles reaching the units in September 1944. About 20% were lost in combat, with most destroyed by their crews when abandoned because of breakdowns or lack of fuel.
 The gun used two-part ammunition, which meant that the main projectile and the cased propellant-charge were loaded into the breech separately. Two loaders were tasked with this work, one for each type.
 Tiger I tank ace Otto Carius commanded the second of three companies of Jagdtigers in s.Pz.Jg.Abt. 512. His postwar memoir Tigers in the Mud provides a history of the 10 Jagdtigers under his command. He said the Jagdtigers were not utilized to their potential due to factors including Allied air supremacy making it difficult to maneuver and the heavy gun needing to be re-calibrated after travelling off-road even short distances. The vehicle was slow, having the same engine as the already-underpowered Tiger I and Tiger II. The vehicles' transmissions and differentials broke down easily because the whole 72-tonne vehicle needed to rotate for the gun's traverse. The enormous 128 mm main-gun had to be locked down during the vehicle's maneuvers, otherwise its mounting-brackets would wear out too much for accurate firing afterwards. This meant a crew-member had to exit the vehicle in combat and unlock the gun from its frontally mounted gun travel-lock before firing. Carius recorded that, in combat, a 128 mm projectile went through the walls of a house and destroyed an American tank behind it.
 Insufficient training of vehicle crews and their poor morale during the last stage of the war were the biggest problems for Jagdtiger crewmen under Carius's command. At the Ruhr Pocket, two Jagdtiger commanders failed to attack an American armored column about 1.5 km (1 mile) away in broad daylight for fear of attracting an Allied air attack, even though the Jagdtigers were well-camouflaged. Both vehicles broke down while hurriedly withdrawing through fear of the supposed air attack that did not materialize and one was then subsequently destroyed by its crew. To prevent such a disaster, at Siegen, Carius himself dug in his command vehicle on high ground. An approaching American armored column avoided his ambush because nearby German civilians warned them of it. Later, one of his vehicles fell into a bomb crater at night and was disabled while another was lost to a Panzerfaust attack by friendly Volkssturm militia troops who had never seen a Jagdtiger before and mistook it for an Allied vehicle.
 The first Jagdtiger lost in combat was during the failed Operation Nordwind offensive in France in 1945. Despite its heavy armour, this Jagdtiger was lost to American infantry using a bazooka, which at the time was considered ineffective against such a massive vehicle.
 Near Unna, one Jagdtiger climbed a hill to attack five American tanks 600 meters away, leading to two withdrawing and the other three opening fire. The Jagdtiger took several hits but none of the American projectiles could penetrate the 250 mm (9.8 in) thick frontal armor of the vehicle's casemate. However, the inexperienced German commander lost his nerve and turned around instead of backing down, thus exposing the thinner side armor, which was penetrated and all six crew members killed. Carius wrote that the crews were not trained or experienced enough to keep their thick frontal armour facing the enemy in combat.
 When unable to escape the Ruhr Pocket, Carius ordered the guns of the remaining Jagdtigers destroyed to prevent intact vehicles falling into Allied hands and then surrendered to American forces. The 10 Jagdtigers of the 2nd Company of s.Pz.Jg.Abt. 512 destroyed one American tank for one Jagdtiger lost to combat, one lost to friendly fire, and eight others lost to mechanical breakdown or destruction by their own crews to prevent capture by enemy forces.
 On 17 January 1945, two Jagdtigers used by the Heer's XIV Corps engaged a bunker-line in support of assaulting infantry near Auenheim. On 18 January, they attacked four secure bunkers at a range of 1,000 meters. The armored cupola of one bunker burned out after two shots. A Sherman attacking in a counter-thrust was set afire by explosive shells. The two Jagdtigers survived the fight, having fired 46 explosive shells and 10 anti-tank shells.
 In April 1945, s.Pz.Jäg.Abt. 512 saw a great deal of action, especially on 9 April, where the 1st Company engaged an Allied column of Sherman tanks and trucks from hull-down positions and destroyed 11 tanks and over 30 unarmored or lightly armored targets, with some of the enemy tanks knocked out from a distance of more than 4,000 m. The unit lost one Jagdtiger in this incident, after Allied Republic P-47 Thunderbolt fighter-bombers appeared. During the next couple of days, the 1st Company destroyed a further five Sherman tanks before surrendering to US troops at Iserlohn. Meanwhile, the 2nd Company fought on with little gain. On 15 April 1945, the unit surrendered at Schillerplatz in Iserlohn.
 Three Jagdtigers survive, in US, UK and Russian museums:
 Aside from the 11 early vehicles with a Porsche suspension, the only variant developed was the Sd.Kfz.185.