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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 (an anti-tank weapon) 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 sometime recorded as ROQF from Royal Ordnance (the manufacturer) Quick Firing.
Development
Prior to the introduction of the ROQF 75 mm, British tanks had been equipped with guns such as the QF 2 pdr (later replaced with the 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 the Churchill Mk 1 and CS ("close support") versions of the Matilda tank. 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 the guns scavenged from Sherman tanks and fitted to their turrets to give the Churchill NA75. Approximately 200 were converted in this way. Instead of looking to take the American gun to be fitted en mass into British tanks, the Royal Ordnance modified the 6 pdr design by boring out the barrel and adapting the breech to fire the US round. The resulting gun was effective but in gaining the HE shell came the lack of an effective anti-tank round that 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.
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 QF 6 pdr, some units retained a number of 6 pdr gunned tanks, due to its superior anti tank firepower over the 75 mm, especialy as the 6 pdr had apcr and apds rounds availble.
Externally the gun was nearly identical to the QF 6 pdr gun. The 14.9 lb (6.76 kg) HE shell fired at 2050 ft/s (625 m/s) was found to be the best available - superior to that of the QF 6 pdr, M7 76.2 mm 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 the APCBC shot (Armour Piercing Capped, Ballistic Cap). 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. One modelling website refers to the 75 mm with the phrase "10 pounder" with an AP performance of 124 mm at 100 yards (90 m). This could be a nickname for the ROQF 75 mm, or a typographical error for the 8 pounder, a gun that was never issued. According to some British tables M72 AP had a penetration performance of 114mm at 100 yards and 102mm 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 101mm at 100 yards. Hunnicuts Shermans has the story the British army re-cartridged the round with cartridges based on the German L 24 75mm gun, with around 3.2 pounds of propellant instead of the standard 2 pounds which could explain this.
- 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 |
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.
External links
References
- US Document WO 219/2806, Appendix G to SHAEF/16652/GCT/Arty,
- "Fire and Movement", Bovington Tank Museum
See also
"Ordnance QF 75 mm"