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.