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 destroyers. 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 790 m/s as opposed to 750 m/s 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 IVs 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 calibers 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 750 m/s, 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 770 m/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. 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.

General characteristics

 * Caliber: 75 mm
 * Barrel length: L/46
 * Rifling: 32 Grooves, right-hand increasing twist, 1/24 to 1/18.
 * Length with the carriage: 6.2 m
 * Length: 3.45 m
 * Width: 2 m
 * Height: 1.25 m
 * Weight (combat ready): 1425 kg
 * Traverse: 65°
 * Elevation: -5° to + 22°
 * Rate of fire: 14 rounds per minute
 * Engagement range: 1800 m
 * Indirect range: 7678 m m (HE shell)
 * Projectile weight: 3.18 kg to 6.8 kg

Survivors
Pak 40s are or have been lately held in several military museums, outside museums or free entrance open-air fields