The 7.5 cm Pak 40 (7,5 cm Panzerabwehrkanone 40) was a German 75-millimeter anti-tank gun developed in 1939-1941 by Rheinmetall and used during the Second World War.
The Pak 40 formed the backbone of German anti-tank guns for the latter part of World War II, mostly in towed form, but also on a number of tank destroyers such as the Marder series. Approximately 20,000 Pak 40s were produced.
A modified version of the gun designed specifically for vehicle-mounting was the 7.5 cm KwK 40, which differed primarily in using more compact ammunition, thereby allowing more rounds to be carried inside the vehicles.
The KwK 40 armed many of the German mid-war tank and destroyer designs, replacing the Pak 40 in the latter role.
Depending on the source, the Pak 40 may be referred to as the 7.5/L46, referring to the barrel’s length in calibers. There were two versions of the KwK 40, which would be referred to as the 7.5/L43 or 7.5/L48.
Development of the Pak 40 began after reports of new Soviet tank designs began to reach Berlin in 1939. The 5 cm Pak 38 was still in testing at this point, but it appeared it would not be powerful enough to deal with these newer designs.
Contracts were placed with Krupp and Rheinmetall to develop what was essentially a 7.5 cm version of the Pak 38. However, while the Pak 38 made extensive use of light alloys to reduce overall gun weight, these were now earmarked for Luftwaffe.
As a result, the Pak 40 used steel throughout its construction and was proportionally heavier than the 5 cm model. To simplify production, the Pak 38’s curved gun shield was replaced by one using three flat plates.
The project was initially given low priority, but following the invasion of the USSR in 1941 and the appearance of heavily armored 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.
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 war, the Pak 40 remained in service in several European armies, including Albania, Bulgaria, Czechoslovakia, Finland, Norway, Hungary, and Romania.
About 20,000 Pak 40s were produced, and about 3,500 more were used to arm tank destroyers. The unit manufacturing cost amounted to 2,200 man-hours at 12,000 RM.
A lighter automatic “weapon system” version incorporating a twelve-round magazine, the heaviest of the Bordkanone series of heavy calibre aircraft guns, was used as the BK 7,5 in the Henschel Hs 129B-3 and the Junkers Ju 88P-1 ground attack aircraft, and even intended as a production fitment for a possible He 177A-3/R5 heavy bomber adaptation late in 1942, originally prototyped in the field with BK 5 cannons, themselves adapted from the 5 cm KwK 39 tank gun from the Panzer III.
The weapon was effective against almost every Allied tank until the end of the war. The Pak 40 was much heavier than the 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 the USSR where it was needed to combat the newest Soviet tanks. It was designed to fire the same low-capacity APCBC, HE and HL projectiles that had been standardized for use in the long-barrelled Kampfwagenkanone KwK 40 tank-mounted guns of the mid-war and later marks of the Panzer IV medium tank.
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.
According to the German Panzertruppen News Journal, 5,000 APCR rounds were expected in Dec. 1942 as replenishment for the Winter offensive.
The main differences amongst the rounds fired by 75 mm German guns were in the length and shape of the cartridge cases as well as the primers used.
The 7.5 cm KwK 40 (75x495mm) used in tanks had a fixed cartridge case twice the length of that used by the 7.5 cm KwK 37, the short-barrelled 75 mm used on earlier tanks, and the 7.5 cm Pak 40 cartridge was a third longer than that used by the KwK 40.
The Pak 40 used a percussion primer, while the vehicle-mounted 75 mm guns used electrical primers.
Other than minor differences with the projectiles’ driving bands, all German 75 mm guns used the same 75mm projectiles.
The longer cartridge case of the Pak 40 allowed a larger charge to be used and a higher velocity for the PzGr 39 armor-piercing capped ballistic cap round to be achieved.
The muzzle velocity was about 790 m/s (2,600 ft/s) as opposed to 740 m/s (2,400 ft/s) for the KwK 40 L/43 and 750 m/s (2,500 ft/s) for the L/48.
The only 75mm fighting vehicle gun in general use by Germany that possessed a longer barrel than the Pak 40, the 7.5 cm KwK 42 on the Panther tank, could achieve a higher muzzle velocity of 935 m/s (3,070 ft/s) on what was essentially the same calibre and model of the shell, with a differing propellant cartridge fixed to it for the KwK 42’s use.
For unknown reasons, some 75 mm APCBC cartridges appear to have been produced with a charge that gave a muzzle velocity of about 770 m/s (2,500 ft/s).
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.
Postwar 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.
*This article was originally published at en.wikipedia.org