Resembling a barrel with a pair of ironing boards for wings, the American-designed and -built Grumman Martlet I was the first aircraft in British service armed with medium-calibre guns. These aircraft were taken over from a French order, and at the Air Ministry’s behest the armament of six rifle-calibre guns was changed for four of medium calibre.

Самолёты на фотографии: Aircrafts on the photo: Grumman F4F Wildcat - СШАUSA - 1937

The 15 British-built Hawker Hurricanes that were in active service with the Belgian Air Force in the spring of 1940, one of which is seen here, were fitted with four 0-303in guns per wing. The Belgian-built aircraft were fitted with two 13-2mm FN guns per wing. Only one of the Belgian-built examples was delivered before Belgium fell, however, and was allocated to the test centre at Evere, so it is unlikely it saw action.

Самолёты на фотографии: Aircrafts on the photo: Hawker Hurricane - ВеликобританияUnited Kingdom - 1935

Arming an RCAF North American Mustang I in 1944. When the Mustang I was introduced into RAF service in the spring of 1942, it was fitted with a mixture of American “30-cal" (not British 0-303in) and “50-cal” Colt machine-guns; one 0-5in and two 0-3in guns in each wing and a pair of cowling-mounted 0-5ins which fired through the propeller arc, seen here.

Самолёты на фотографии: Aircrafts on the photo: North American P-51 Mustang - СШАUSA - 1940

A USAAF North American A-36 being re-armed in North Africa in 1943 with medium-calibre “50-cal” ammo; the British were then still using 0-303in machine-guns.

Самолёты на фотографии: Aircrafts on the photo: North American P-51 Mustang - СШАUSA - 1940

The wing gun bay of a Mustang I, showing the two smaller “30-cal” machine-guns and their feeds outboard (i.e. to the left) of the larger “50-cal”. The much larger size of the 0-5in round is apparent, as is the awkwardness of arranging the ammunition supply in the available space with contemporary solid (i.e. inflexible) feed-chutes.

Самолёты на фотографии: Aircrafts on the photo: North American P-51 Mustang - СШАUSA - 1940

In March 1943 the RAF evaluated the North American A-36, the dedicated ground-attack version of the Mustang, one example, EW998, being put into British markings for testing.The A-36 replaced the Mustang I’s mixed 0-3in/0-5in armament with six 0-5in Browning machine-guns; two in each wing and two in the cowling. The type was not adopted for RAF service, however.

Самолёты на фотографии: Aircrafts on the photo: North American P-51 Mustang - СШАUSA - 1940

In marked contrast to the cramped, untidy wing armament layout of the Mustang I, the three 0-5in machineguns mounted in each wing of the RAF’s Merlin-powered Mustang Mk IVs (which had no cowling-mounted guns), were fitted with flexible feed-chutes, allowing the guns to be mounted upright rather than at an awkward angle.

Самолёты на фотографии: Aircrafts on the photo: North American P-51D Mustang - СШАUSA - 1944

The Fairey Fulmar entered service with the Fleet Air Arm in June 1940, the first of the Service’s fighters to have eight (0-303in) guns. Late Fulmars, including the comparatively few Fulmar NF.2s, of which one is seen here, were fitted with an updated armament of four 0-50in guns, making them the only British fighter in FAA service to use the medium-calibre gun during the Second World War.

Самолёты на фотографии: Aircrafts on the photo: Fairey Fulmar / P.4/34 - ВеликобританияUnited Kingdom - 1937