War ended. The new gun and carriage was in effect a new weapon but as the calibre and ammunition remained the same it was referred to as part of the 18 pr development cycle until the calibre was phased out. By 1919, the standard British field gun was the 18-pounder Mk IV gun on Mk IV carriage but Britain still possessed many of the older Marks. Naval Use In addition to its land role 184 guns were converted to arm Defensively Armed Merchant Ships (DAMS) against U-boat attack during the First World War. The conversion entailed mounting the guns on the same type of elastic mount used by the QF 6-pounder Hotchkiss. Wagons and Limbers The "carriage" limber, towed between the gun and horse team, carried 24 rounds of ammunition. Each gun was accompanied by a second horse team towing an ammunition wagon and wagon limber carrying the gun detachment (none were carried on the gun limber) and 38 rounds in each. In action, the wagon was placed close beside the gun; its steel body provided an extended shield to protect the detachments against small arms fire. The towed weight of the gun and loaded limber was 40 cwt (2,000 kg), the wagon and its limber were about 37 cwt. Each battery also held a second wagon and wagon limber per gun, giving first line ammunition stocks of 176 rounds per gun. Inter-War Period On 28 June 1922, Michael Collins effectively started the Irish Civil War by using two 18-pounder field guns, "borrowed" from the British Army, to bombard the Four Courts in Dublin. The Mk V carriage with split trail entered service in 1923, it allowed 25 degrees left and right traverse without moving the trail and up to 37.5 degrees elevation. In the same year the Army began a full-scale mechanisation of the artillery: Vickers Medium Dragon tracked artillery tractors were used to tow the gun, and the horse teams began to be returned to the Army Remount Service. In 1925, some guns were experimentally fitted on a Medium tank chassis as self-propelled artillery (the "Birch gun"), the Birch gun was used for the exercises of the Experimental Mechanized Force in 1927–1928. The Mk IV ordnance was modified. In the Mk IVA, the A tube and wire were replaced by an autofrettaged loose liner. The Mk IVB was the same with minor modifications, most notably 3 shoulders instead