In September 1934 a pilot model for a new 25 pdr Gun was ordered. To keep down costs it was decided to produce an auto-frettaged loose barrel that could be inserted into the jacket of the existing 18 pdr. This would then be fitted to the 18 pdr Mark 4P or Mark 5P carriage. This became known as the 25 pdr Gun Mark 1 (18/25 pdr). At the same time development continued on a complete 25 pdr gun and carriage hoping funds would become available later.
Official approval for the 18 pdr conversion was given on 26th August 1936 as the Ordnance QF 3.45 inch Mark 1. In February 1938 this was changed to Ordnance QF 25 pdr Mark 1. However it was mostly known by the name ’18/25 pdr’ as this was the more accurate description. Over 1,000 of the 25 pdr Gun Mark 1 (18/25 pdr) were produced.
Data
| Weight of gun & breech mechanism | 991 lbs |
| Total length | 96.725 inches |
| Length of Bore | 92.365 inches |
| Rifling | Polygroove, plain section |
| Firing mechanism | Percussion |
Performance
| Muzzle velocity | 1486 feet per second |
| Maximum range | 11,500 yards |
Ammunition
As for the 25 pdr Mark 2 except Supercharge could not be fired