The BL 4.5 inch medium gun was a British gun used by field artillery in the Second World War for counter-battery fire. Developed as a replacement for the BL 60-pounder gun it used the same carriage as the BL 5.5-inch medium gun but fired a lighter round further. It had nothing in common with the QF 4.5 inch Howitzer or the QF 4.5 inch AA gun. Development By the end of the 1930s, the First World War-era (5-inch calibre) BL 60-pounder gun Mk. I of 1905 and Mk. II of 1918 (two different designs) had become obsolete, and their barrels had mostly reached the end of their usable service life. A successor was sought and work began on an all-new design that would result in the Ordnance BL 4.5 inch medium field gun, a long-range medium gun designed for counter-battery fire. The gun was in use throughout the Second World War and it equipped a number of medium regiments, including half the Canadian ones. In service, the guns were fielded at the regiment level and were taken on by both British and Canadian artillery field groups during the war. The 4.5 inch field gun was a good weapon that could fire a 25 kg HE shell up to 11.6 miles with Charge 3. It matched German 10.5 cm and 150 mm howitzers in range and firepower. For the sake of expediency, Mk I ordnance was designed to be mounted on the 1918 60-pounder carriage. The Mk I gun was first issued in 1938 and equipped one or two regiments of the British Expeditionary Force. The 4.5 inch Mk I due to lack of visual clues is sometimes mistaken for the 60-pounder. The Mk II was on a new carriage that was also used with the BL 5.5 inch medium gun (which was being developed at the same time to replace the BL 6-inch 26 cwt howitzer). There were slight differences between the Mk 1 and Mk 2 equipment, but the maximum range was almost identical. Issues of the Mk 2 ordnance on the common carriage started in 1941. Service The Mark I was used in the Battle of France in 1940. They also equipped at least one regiment in the North Africa campaign and some were lost during the Battle of Greece. The Mk II gun served in North Africa, Italian campaign and North West Europe. It was withdrawn from