7 . 5 cm Pak 40 The 7 . 5 cm Pak 40 ( " 7 . 5 cm Panzerabwehrkanone 40 " ) was a German 7 . 5 centimetre anti - tank gun developed in 1939 - 1941 by Rheinmetall and used during the Second World War . Pak 40 formed the backbone of German anti - tank guns for the latter part of World War II . Development . Development of the Pak 40 began in 1939 with contracts being placed with Krupp and Rheinmetall to develop a 7 . 5 cm anti - tank gun . Priority of the project was initially low , but following the invasion of the USSR in 1941 and the unexpected appearance of heavily armoured Soviet tanks such as the T - 34 and KV - 1 , it was given an increased priority . The first pre - production guns were delivered in November 1941 . In April 1942 , the " Wehrmacht " had 44 guns in service ; by 1943 the Pak 40 formed the bulk of German anti - tank artillery . Operational use . The Pak 40 was the standard German anti - tank gun until the end of the war , and was supplied by Germany to its allies . Some captured guns were used by the Red Army . After the end of the war the Pak 40 remained in service in several European armies , including Albania , Bulgaria , Czechoslovakia , Finland , Norway , Hungary and Romania . About 23 , 500 Pak 40s were produced , and about 6 , 000 more were used to arm tank destroyer s . The unit manufacturing cost amounted to 2 , 200 man - hours at 12 , 000 RM . A lighter automatic version , the heaviest of the " Bordkanone " series of heavy calibre aircraft guns , was used as the " BK 7 , 5 " in the Henschel Hs 129B - 3 ground attack aircraft and the Junkers Ju 88P - 1 bomber destroyer . Performance . The weapon was effective against almost every Allied tank until the end of the war . The Pak 40 was much heavier than the 5 cm Pak 38 ; its decreased mobility meant that it was difficult or even impossible to move without an artillery tractor on boggy ground . The Pak 40 was first used in Russia where it was needed to combat the newest Soviet tanks . It was designed to fire the same low - capacity APCBC , HE and HL projectiles which had been standardized for use in the long barreled " Kampfwagenkanone " KwK 40 tank - mounted guns . In addition there was an APCR shot ( " Panzergranate " 40 ) for the Pak 40 , a munition which - reliant on supplies of tungsten - eventually became very scarce . The main differences amongst the rounds fired by 75 mm German guns were in the length and shape of the cartridge cases for the Pak 40 . The 7 . 5 cm KwK ( tank ) fixed cartridge case is twice the length of the 7 . 5 cm KwK 37 ( short barrelled 75 mm ) , and the 7 . 5 cm Pak 40 cartridge is a third longer than the 7 . 5 cm KwK 40 . The longer cartridge case allowed a larger charge to be used and a higher velocity for the armour - piercing capped ballistic cap round to be achieved . The muzzle velocity was about as opposed to for the KwK 40 L / 43 . This velocity was available for about one year after the weapon ' s introduction . Around the same time , the Panzer IV s 7 . 5 cm KwK 40 L / 43 gun and the nearly identical " Sturmkanone " ( StuK ) 40 L / 43 began to be upgraded with barrels that were 48 caliber s long ( L / 48 ) , which remained the standard for them until the end of the war . In the field , an alarming number of L / 48 cartridge cases carrying the hotter charge failed to be ejected properly from the weapon ' s semi - automatic breech , even on the first shot ( in vehicles ) . Rather than re - engineer the case , German Ordnance reduced the charge loading until the problem went away . The new charge brought the muzzle velocity down to , about 10 m / s higher than the original L / 43 version of the weapon . Considering the average variability in large round velocities from a given gun , this is virtually negligible in effect . The first formal documentation of this decision appears on May 15 , 1943 ( " 7 , 5cm Sturmkanone 40 Beschreibung " ) which details a side - by - side comparison of the L / 43 and the L / 48 weapons . The synopsis provided indicates very little difference in the guns , meaning the upgrade had little if any benefit . All further official presentations of the KwK 40 L / 48 ( " " Oberkommando des Heeres , Durchschlagsleistungen panzerbrechender Waffen " " ) indicate a muzzle velocity of 750 m / s for the gun . As for the Pak 40 , the desire for commonality again appears to have prevailed since the APCBC charge was reduced to 750 m / s , even though case ejection failures were apparently never a problem in the Pak version of the gun . For unknown reasons some 75 mm APCBC cartridges appear to have been produced with a charge which gave a muzzle velocity of about . The first documented firing by the US of a Pak 40 recorded an average muzzle velocity of 776 m / s for its nine most instrumented firings . Probably because of these results , period intelligence publications ( " Handbook on German Military Forces " ) gave about 770 m / s as the Pak 40 APCBC muzzle velocity . Post war publications corrected this . German sources differ ; the Official Firing Table document for the 75 mm KwK 40 , StuK 40 , and the Pak 40 dated October , 1943 gives 770 m / s on one of the APCBC tables . Survivors . Pak 40s are or have been lately held in several military museums , outside museums or free entrance open - air fields