During World War 1, British and Commonwealth artillery regiments relied on their trusted BL 6-inch 26 cwt series medium field howitzers. The guns were large systems of 152.4 caliber, weighing in at 8,100lbs and requiring a crew of 10 personnel to manage. The weapon fired high-explosive, incendiary and gas projectiles at a maximum rate of 2 rounds per minute out to 9,500 yards. Multiple manufactures banded together to supply forces with some 3,633 examples while the weapon remained in service well into 1945 - this being the final year of World War 2.
However, by 1939, the weapon was more or less an obsolete option from an era since passed. As such, the British Army sought its capable though altogether modern replacement and enacted a new requirement for a medium-class field gun with expanded capabilities. Design work ensued and prototypes were successfully tested to bring about the new weapon - the 140mm "BL 5.5-inch Medium Gun". The weapon was delivered to British artillery elements in the middle part of 1941 - Britain had already declared war on Hitler's Germany on September 3rd, 1939 and recently successfully fought for its very survival throughout the summer of 1940 in the Battle of Britain. Serial production of the field gun spanned from 1941 to 1945 and provided a much-needed punch for British and allied field units against the might of the Axis powers wherever they were to meet.
Design of the BL 5.5 was quite conventional as artillery systems go. The weapon essentially involved a few key pieces forged into a single fine instrument of war. The weapon consisted of the gun barrel with its breech, the gun mounting and the carriage. Other key components then became the requisite gunnery crew as well as the towing vehicle needed to transport the weapon from site to site. The barrel mechanism was tied to a hydro-pneumatic recoil system to help counter the violent forces of the exiting shell. The crew managed loading and reloading through a Welin breech mechanism . The weapon sat upon a two wheeled split carriage to which the legs were either brought together for transport or spread apart when firing. Elevation of the main gun ranged from -5 degrees to +45 degrees with traverse limited to 30-degrees left or right. Beyond that, the gunnery crew would have to physically rotate the entire system in a given direction prior to firing. A trained crew could fire approximately 2 rounds per minute. A complete gunnery crew included 10 men with several required just to manage the large shells.
The BL 5.5 was cleared to fire two distinct projectile sizes - an 82lb shell and a 100lb shell. The 82lb shell sported a muzzle velocity of 1,950 feet per second with a range out to 18,000 yards. Comparatively, the 100lb shell measures a muzzle velocity of 1,675 feet per second with a maximum range of 16,200 yards. The originally design projectile was the 100lb variety as the 82lb shell was not introduced until 1944. The lighter shell with increased charge allowed for the extension of range and was also branched into a smoke, illumination and chemical round to further broaden its tactical reach.
The BL 5.5 series went on to see extensive combat service with British and Commonwealth forces throughout World War 2 including actions in the large scale El Alamein engagements. It was featured once more in the upcoming Korean War of the early 1950s in which United Nations forces were pitted against North Korea, China and the Soviet Union - ultimately ending in a shaky armistice. Additional actions included its use in the Borneo Conflict (1962-1966) while non-British combat use of the weapon extended to the North Yemen Civil War (1962-1970) and the Angolan Civil War (1975-2002).
Beyond its service in the British Army, the BL 5.5 series went on to see extended lives in Commonwealth armies as well - Australia, Canada, India, New Zealand and South Africa all made use of the type as a frontline implement. It was further operated by the forces of Burma, France, Iraq, Malaysia, Oman, Pakistan, Poland and Portugal in the post-war years. Only four production marks of the BL 5.5 were eventually adopted and only the Mk 3 saw combat service in World War 2 - the Mk 4 followed in the post-war years.
For the British Army, the BL 5.5 was eventually replaced in service by the modern FH-70/L121 155mm series beginning in 1978. British use, therefore, discontinued in 1980 while the Australians followed suit in 1984 - though electing the American M198 as its replacement.