By World War 2 (1939-1945), the World War 1-era BL 60-pounder (detailed elsewhere on this site) of 1905 had reached the end of its usable service life within the ranks of the British Army. As such a successor was sought and work began on an all-new design. This initiative resulted in the Ordnance BL 4.5" Medium Field Gun which went on to see service through to the end of World War 2.
Compared to the heavy-class BL 60-pounder before it, the medium-class BL 4.5" fired a slightly lighter projectile of 114mm caliber. It featured a Welin (stepped, interrupted thread) breech design coupled to an Asbury breech open-close mechanism (a breech similar to that as encountered on naval guns of the period). The complete weapon system weight 12,880lb and the barrel measured 15.4 feet long.
The gun tube was set atop mounting hardware affixed to a split-trail carriage system straddled by a pair of rubber-tired road wheels. For the sake of expediency, this carriage was the same as used in the BL-60-pounder units. The trail legs were closed when the unit was in transport and opened when the weapon was made ready to fire. Wheels along the mounting section were used to achieve the desired traverse and elevation of the gun tube. An integrated recoil mechanism allowed the weapon to remain relatively stationary when the firing action occurred. The shell was of High-Explosive content weighing 55lb. It exited the muzzle of the gun tube at 2,250 feet-per-second and held a maximum range out to 20,500 yards. Sighting was by way of an integrated unit.
In service, the new guns were fielded at the regiment level and were taken on by both British and Canadian artillery field groups during the war. The initial production form became the Mk 1 and these saw issuance begin prior to the war in 1938. They saw their baptism of fire in the early phases of the conflict in the hands of the British Expeditionary Force (BEF) fighting in France and elsewhere. A stock was also shipped to British elements in the North Africa campaign and a further number were committed to the battles in Greece.
In 1941, the 114mm gun was set atop a standardized carriage common to 4.5" and 5.5" systems. This created the Mk 2 designator and many were fielded in the fighting of North Africa as well as the Italian Campaign and in the subsequent post-invasion period across France, Belgium and Holland. The type acquitted itself rather well on varied battlefields of the war and served until the final days of the years-long conflict. In 1945, the series was retired from front-line service and the remaining stock were used as training tools It was finally declared wholly obsolete in 1959, brining an official end to the line.