Ordnance QF 75 mm

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The Ordnance QF 75 mm, abbreviated to OQF 75 mm, was a British tank-gun of the Second World War. It was used instead of the Ordnance QF 6 pounder ("6 pdr"), an anti-tank gun, to give better performance against infantry targets in a similar fashion to the 75 mm gun fitted to the American Sherman tank. The QF came from "quick firing". The gun was also sometimes known as ROQF from Royal Ordnance (the manufacturer) Quick Firing.

1 Development
2 Service
3 Similar named guns
4 External links
5 References
6 See also

[edit] Development

Prior to the introduction of the ROQF 75 mm, British tanks had been equipped with guns such as the QF 2 pounder, and then the larger 6 pdr, that fired Armour Piercing shot - good against tanks but ineffective against groups of infantry. Some tanks operating in the infantry support role were given guns firing HE shells, eg early models of Churchill tank and CS ("Close Support") versions of the Matilda II. The decision to equip British tanks with an HE shell firing gun for "soft" targets like infantry and, importantly, anti-tank guns was taken by the War Office.

An HE shell for the 6 pounder was in production by the time of the start of the Tunisian campaign and available in large amounts in the Italian Campaign. However, the round lacked sufficient explosive power. The power of the US 75 mm HE round used in the M3 75 mm was found to be markedly superior, and a number of Churchills in operation in Italy had guns scavenged from Sherman tanks and fitted to their turrets to give the Churchill NA75 (NA coming from "North Africa" where the conversions were carried out). Approximately 200 were converted in this way. Instead of looking to take the American gun to be fitted en masse into British tanks, the Royal Ordnance modified their 6 pdr design by boring out the barrel and adapting the breech to fire the US round. The resulting gun was effective but although gaining a good HE shell they had an inferior anti-tank round and this proved troublesome against the well armoured German tanks. In the Battle of Villers-Bocage Cromwell tanks with the 75 mm were no match in battle with a lone Tiger tank.

[edit] Service

The ROQF 75 mm was chiefly used on the Churchill and Cromwell tanks. The weapon was used in Italy and Normandy (and possibly in Burma against the Japanese) until the end of the war. While the 75 mm was a conversion from the 6 pounder, some units retained a number of 6 pounder gunned tanks, due to its superior anti tank firepower over the 75 mm, especially as the 6 pounder could use the even more effective APCR and APDS rounds.

Externally the gun was nearly identical to the 6 pounder gun. The 14.9 lb (6.76 kg) HE shell fired at 2,050 ft/s (625 m/s) was found to be the best available - superior to that of the 6 pounder, M7 3 in and 17 pounder all chiefly anti-tank guns. However, against armour its AP shell was the worst, penetrating only 68 mm of RHA at 500 yards (460 m) and a 30 degree angle of attack, whereas the AP shells of the others penetrated between 87 mm and 125 mm in Normandy during 1944. The AP shell for the 75 mm gun was a 15 lb (6.8 kg) projectile with a couple of ounces (60 g) of HE filling propelled by a 2 lb (900 g) charge to 2,000 feet per second (610 m/s). In British service the AP shell was used without its explosive filling and as such was referred to as "AP Shot M61".

A much improved anti tank shell was developed. This was a APCBC (Armour Piercing Capped, Ballistic Cap) shot design. It had a muzzle velocity of 2,600 ft/s (790 m/s) as opposed to 2,030 ft/s (620 m/s) for the older M61 APC shell. US documents¹ showed the round as available for both the M3 75 mm and ROQF 75 mm. Other sources² indicate the shell saw use by the British only. The performance of the new shell was a vast increase: penetrating 102 mm at 500 yards (460 m) at 30 degree angle of impact. Actual availability and usage of this round is unclear. According to some British tables M72 AP had a penetration performance of 114 mm at 100 yards and 102 mm at 500 yards, so it is possible the 30 degrees angle of impact is a transposition error for 0 degrees. This is interesting as US M72 has a penetration performance of 101 mm at 100 yards.

Comparison with the other guns

Gun	Shell weight		Muzzle velocity
	(lb)	(kg)	(ft/s)	(m/s)
2 pdr	2	0.9	2,650	810
6 pdr	6	2.7	3,000	910
75 mm	14.9	6.8	2,050	620
17 pdr	17	7.7	2,950	900

[edit] Similar named guns

In the First World War some French 75 mm field guns used by the British forces received the designation Ordnance QF 75 mm Mk I. And in the early part of the Second World War some American 75 mm Gun M1897A3 field guns were purchased from the US. these would also have been referred to as Ordnance 75 mm.