The 465-page full text "History of the Indian Mountain Artillery" (first published 1957) can be downloaded here:
Therein is contained much information about the Indian Mountain Artillery during WW2; of interest to this forum is the war fought by the IMA in Malaya and Burma and its use of the 3.7-inch howitzer and the (so-termed) Breda 2-pounder AT gun. Also references to the 2.75-inch mountain gun - not the 2.95" (Vickers 75mm) acquired by the US for use in the Philippines. The 2.95-inch mountain gun was used by a few African colonies but was not adopted by the British Army or the Indian Army.
The Quick Firing 3.7-inch mountain howitzer was specifically developed at the request of the Indian Army and superseded the 2.75-inch gun, when it was introduced in 1917. During WW2 production was transferred to India and about 800 pieces built. South Africa also produced a good number (190 howitzer, 101 pack howitzer) during early-1941, most of which were exported to India and Burma. My take on this is that the ISCOR (Iron and Steel Corporation of South Africa)-produced 3.7s were intended for use by SA forces in the mountainous regions of Abyssinia during that campaign, but this had ended before the guns could be delivered. South African artillery units were by then equipped with heavier weaponry and had no further use for the 3.7s - these were therefore sent to the East.
Below is an example exhibited at Queen's Fort Military Museum in Bloemfontein of a QF 3.7-inch Mk.IV P (P = Pneumatic Tyres) SAP - South African Pattern?
From the text it appears that for much of the war, Indian Mountain Artillery units were only partly mechanised and most guns continued to be of the wooden wheeled types - lighter and easier to carry in pack, and to man-handle when the terrain made the use of motor transport impossible. Mules as pack animals were used extensively until the end of the war, obtained from South Africa or under Lend-Lease arrangements (!), from the US. The 3.7-inch howitzer was found to be ideally suited for conditions in Burma and equipped all Indian Mountain Artillery regiments as well as some light field units of the Royal Artillery. The term "Jungle Regiment" was sometimes used - these equipped with a mix of pneumatic wheeled 3.7s and 3-inch mortars.
Royal Artillery gun detachment preparing to fire a 3.7-inch howitzer during the Battle of the Ngakyedauk Pass, Arakan, February 1944.
The 3.7 saw use in almost all theatres during WW2, including on Guadalcanal by Royal New Zealand Artillery and in New Guinea by Royal Australian Artillery.
Australian troops load 3.7-inch mountain howitzers onto a captured Japanese barge on 15 November 1942. It is likely that they were being loaded at Biamu, Oro Bay, for transport up the coast closer to Buna, New Guinea. It is possible that these soldiers are from O'Hare Troop of the 1st Australian Mountain Battery. From:
Well, that's my 2 cents - at the current exchange rate about 0.07 US cents worth!