The following information is a brief summary taken from Wikipedia following their Re-use of text guidelines. I commend their pages for those interested in the full history of this versatile artillery piece.
The Ordnance QF 25 pounder, or more simply, 25-pounder or 25-pdr, was introduced into service just before World War II, during which it served as the major British and Australian field gun/howitzer. It was considered by many to be the best field artillery piece of the war, combining high rates of fire with a reasonably lethal shell in a highly mobile piece. It was the British Army's primary artillery field piece well into the 1960s, with smaller numbers serving in training units until the 1980s. Many Commonwealth of Nations countries used theirs in active or reserve service until about the 1970s.
The 25 pounder was the main field artillery weapon used by British Commonwealth and colonial (includes Australian) infantry and armoured divisions of all types during the Second World War. Throughout the war each British-pattern infantry division was established with seventy-two 25 pounders, in three field artillery regiments. Armoured divisions eventually were standardised with two field artillery regiments, one of which was self-propelled. Before mid-1940 each regiment had two batteries of twelve guns; after that date, each regiment had three batteries of eight guns each. In the late 1950s, the British Army reverted to batteries of six guns. Field artillery regiments had two batteries of 25 pounders and one of 5.5 inch guns.
The first shot fired by US artillery against the German army in World War II was fired by a 25pdr of the 34th Infantry division.
I have included a photo of An Australian 25 Pounder of the 2nd/8th Field Regiment, Royal Australian Artillery at the Battle of El Alamein in July 1942 from Wikipedia.
This gun is on loan from the Northern Territory Museum, probably in perpetuity as long as the Returned Services League Club remains there.