The 12.8 cm Pak 44, (Panzerabwehrkanone) was a German heavy anti-tank gun used during World War II. It was designed as a result of experiences on the Eastern front in 1943. The German army had encountered the Russian 122 mm guns and had issued a requirement for a similar weapon. Development initially concentrated on a field gun known as the Kanone K 44. However once heavier Russian armour such as the IS-2 started to appear the design requirements were altered to include an anti-armour role. Contrary to some claims this design had nothing in common with the 128 mm FlaK gun.The choice of 128 mm was made because of the availability of tooling due to the use of this caliber on naval weapons, design contracts being awarded to Rheinmetall Borsig and Krupp, the first prototype guns were delivered for testing in late 1944. After initial tests the Rheinmetall design was dropped and development continued with the Krupp design. However the service tests showed that a towed anti-tank gun weighing nearly 11 tonnes was impractical so the towed design was terminated.
Approximately 50 barrels and breeches were used on existing carriages. The weapon that used the ex-French GPF-T carriage was known as the K 81/1 while the K 81/2 used the ex-Russian carriage. Both of these designs were rushed, and were too heavy, making them cumbersome to deploy. In 1943 the design was started for a gun to mount on the Jagdtiger (Sd.Kfz. 186) and the Maus super-heavy tank was started using the Pak 44 as its starting point. This weapon of which approximately 100 were made was known both as the Pak 44 and Pak 80 / Panzerjägerkanone Pjk 80. Performance was identical to the initial design.
The gun was fed with two-piece ammunition, the projectile and cartridge making up separate pieces. Because of this the gun could be fired using three different sized propellant charges, a light, medium and heavy charge. The light and medium charges were normally used when the gun was fulfilling the role of an artillery piece, where they would launch the ~28 kg projectiles to a muzzle velocity of 845 m/s and 880 m/s respectively. Finally the heavy charge was used when the gun was fulfilling its intended role as an anti-tank gun, where it fired a 28.3 kg APCBC-HE projectile (PzGr.43) at a muzzle velocity of 935 m/s. With the heavy charge, and using the PzGr.43 projectile, the PaK44 was capable of penetrating just over 200 millimetres (7.9 in) of 30 degree sloped armor at 1000 meters, and 148 millimetres (5.8 in) at 2,000 metres (2,200 yd) range. But although its short-range performance was similar to the 8.8 cm PaK 43, the 12.8cm PaK 44 better maintained its performance over longer ranges.
The 12.8cm PaK44 ended up becoming the standard main armament for the Jagdtiger heavy tank destroyer, as well as being the planned main armament for most of the future heavy tank designs in development during the dying months of World War II, including the Maus and E-100.