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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 obtained by boring out the Ordnance QF 6 pounder ("6 pdr") 57-mm anti-tank gun to 75-mm, 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. ==Development== Prior to the introduction of the ROQF 75 mm, British tanks had been equipped with guns such as the QF 2 pounder (40-mm), and then the larger QF 6 pounder (57-mm), 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, e.g. 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 Tunisia 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. Vickers were working on a high velocity 75mm gun to be fitted to British tanks. This took the cartridge case of the 3 inch 20 cwt anti-aircraft gun mated to the US 75mm AP and HE shell. With a barrel length of 50 calibres, it would have about twice the muzzle energy of the US 75mm gun. However the final gun turned out to be too big to fit into the tank that it had been expected to fit.〔(An Alternative 1930s British Tank Gun - And Its Successor ) Anthony G Williams〕 Instead of having to take the American gun to be fitted ''en masse'' into modified British tanks, it was noticed that the US 75mm cartridge was almost the same diameter as the British 6 pounder case. 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 could then be fitted without redesigned tank mountings. It was effective but although gaining a good HE shell they had an inferior anti-tank round and this proved troublesome against the minority of heavily armoured German tanks. In the Battle of Villers-Bocage Cromwell tanks with the 75 mm were outgunned by Tiger tanks of the 101st SS Heavy Tank Battalion. Though the 75 mm had a good HE shell, it was still thought that a more powerful close support weapon was needed and as such the Ordnance QF 95 mm howitzer was agreed for a limited number of tanks.〔''Cromwell Vehicle History and Specification'' 1983 HMSO p. xi〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ordnance QF 75 mm」の詳細全文を読む スポンサード リンク
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