of 2. A Mk V ordnance was designed but does not appear to have entered service. In the 1930s, as the British Army started to fully mechanise, all guns were converted to mechanised towing. Initially, this was by fitting heavy wooden wheels with solid rubber tyres, the carriages becoming Mks IIITR, IVR and VR. Subsequently, wooden wheels were replaced by new axles, steel wheels, pneumatic tyres and modern brakes. The Mk IV and V carriages had a British conversion to produce the Mk IVP and VP on 9.00 X 16" wheels. The Mk IIs, with their pole trails, had the American 'Martin Parry' conversion to produce the Mk IIPA on 7.50 X 24" wheels. Unlike other guns, 18-pounder was not converted to Probert pattern calibrating sights. Introduction of a new streamlined shell, Mk 1C, with a 4/7.5 crh increased maximum range to 11,100 yards with Mks III, IV and V carriages. Starting in 1938, Mk IVP and VP carriages were used for the new Ordnance QF 25-pounder Mk 1. This was a conversion from the 18-pounder Mk IV Ordnance. The calibre was increased from 84 mm to 87.6 mm by changing the liner. Spanish service After WWI, Vickers modified 18-pounder on the Mk. IV carriage to shoot 105-mm shells; this design was license-produced as Obús Vickers de 10,5 cm. modelo 1922 (105/22) at partially Vickers-owned Sociedad Española de Construcción Naval plant; those howitzers fought on the both sides of the Spanish Civil War. After the start of WWII they were modernised with a lengthened (from 22 calibres to 30 calibres) barrel featuring a counterweight at the breech and redesignated as Obús de campaña Vickers de 105/30 modelo 1940 Some 105/30 pieces (but not all) received pneumatic wheels. Production By the outbreak of war in 1914, 1225 guns had been produced, including 99 in India. UK production was by Armstrong Whitworth, Vickers and Woolwich Ordnance factory. During the First World War, these were joined by Beardmore, the Elswick Ordnance Company and, in the US, Bethlehem Steel. In the latter part of the war, component assemblies were produced by various other companies. Total wartime production 1914–1918 was 9908 guns and 6926 carriages. Limited production of both guns and carriages continued between the wars and some carriages for use with 25-pounder Mk 1 were produced in the early part of the Second World War. Combat use First World War Throughout the First World