QF 3.7-inch mountain howitzer

The 3.7 inch howitzer superseded the 2.75 inch mountain gun following the First World War. It was used by mountain artillery regiments of the Royal Artillery and the Indian Artillery, and saw much service on the North West Frontier of India between the wars.

During the Second World War, the weapon equipped artillery units engaged in the North African Campaign (Tunisia), the Italian Campaign, the Kokoda Campaign, and Burma Campaign, and was also used in the Netherlands and Ruhr fighting in 1944–45 by units originally destined for mountain warfare in Greece. In the latter theatre, on occasion the gun was dismantled and manually hauled up to the upper floors of buildings to provide close support in urban fighting. A lightened version was used briefly by airborne formations. Several were supplied to the French Army after 1945; one is on display at the Vietnam Army Museum in Hanoi while another is displayed at the Zone 5 Military Museum, Danang. It was also used on Close Support versions of the A9 and A10 Cruiser Tanks in place of the standard 2 pounder, though mostly to fire smoke shells. During the war the gun, and its ammunition, were also manufactured in other Commonwealth countries, including South Africa, by the ISCOR (Iron and Steel Corporation of South Africa), and India. South Africa also produced modified versions of the gun. The gun was finally declared obsolete by the British Army in 1960, although it had not seen service since 1945.

After the war, the gun was used by French forces during the First Indochina War and by India during the Indo Pakistani wars of 1965 and 1971. The "Mujib Battery" of Bangladesh used this gun in 1971's Bangladesh Liberation War. They were provided by India to the Mukti Bahini.

The weapon was designed to be broken into eight mule loads, for transport over difficult terrain. The heaviest single section is the interrupted screw breech, which weighs Given an open gun position, a practised crew could have the guns unloaded from the mules, reassembled and deployed ready for action in about two minutes. The 3.7 inch howitzer's adjustable suspension system allowed it to be deployed on almost any position, even those too uneven or with too steep a gradient to allow field artillery to be sited. The process of removing the howitzer from a position and reloading it onto the gun mules involved much more lifting and securing loads than deploying it, but could be accomplished in three minutes in favourable conditions. The howitzer has a split trail, the first British weapon to do so, which allows firing at very high angles (a useful feature in mountainous terrain). It also has a large rectangular shield to protect the crew from small arms fire, but this was often omitted to save weight. When it was first introduced, the howitzer had two wooden wheels and was light enough be towed by two horses. Later marks have pneumatic tyres and could be towed by any light vehicle, such as the Bren Carrier or jeep. The propellant casing had five "charge zones", but HE was restricted to no more than "charge four", to prevent premature detonation of the shell. The Australian Army did employ charge five in Papua New Guinea in emergencies – the gun crews referred to it as "O'Hara's charge".