The 7.2 inch Howitzer was developed from the 8 inch Howitzer. In July 1940 there was a severe shortage of heavy artillery and a demand was raised for a new gun of about 8 inch calibre with greater range than the existing 8 inch Howitzer. It also needed to be on the same sort of carriage as the 8 inch Howitzer. In August 1940, trials were carried out to determine how much stress the carriage and recoil system of the 8 inch could stand. As a result, development was started on a 7.2 inch Howitzer firing a 200 lb shell with a maximum muzzle velocity of 1,700 feet per second.
Existing 8 inch Howitzers were taken to workshops where the barrel liner was removed and replaced with a 7.2 inch liner. Alterations were made to the breech mechanisms to suit the new calibre. This new weapon was then introduced as the 7.2 inch Howitzer Mark 1. It was officially approved on the 7th April 1941. A little later, American 8 inch Howitzers were bought and converted to 7.2 inch in the same way.
There was a problem with the recoil as the force was more than the recoil system could absorb fully. As a result the carriage moved backwards on firing and on wet ground this movement could be unpredictable and dangerous with the crew having to stand well clear of the gun before firing. To try and control this movement, large wedges were placed behind the wheels so that on recoiling the gun ran up the slope of the wedge and back down again. Even with these wedges, firing was still daunting for the crew. Early in 1943 it was decided that with Charge 4 the gun was not fully under control and so a search began for a new carriage.
The American 155 mm Gun M1 started to arrive in the UK. Its carriage could be adjusted to take the US 8 inch Howitzer so in April 1943 a trial fitting was made of the 7.2 inch. It was successful and the combination was approved in November 1943 as the 7.2 inch Howitzer Mark 5. At the same time a new, more powerful howitzer was being prepared. A completely new design, 33 calibres long, it was approved and adopted on the 21st December 1943 as the Mark 6 Howitzer. As a result the Mark 5 was never issued for service.
The Mark 6 increased the maximum range by about two miles and became the standard equipment of Heavy Regiments. It remained in service into the 1960’s.
Gun
| Mark 1 | Converted from 8 inch Howitzer Mk 8 |
| Mark 1* | Mk1 repaired by insertion of inner ‘A’ tube into worn barrels |
| Mark 2 | Conversion of ex-US 8 inch Mk 6 |
| Mark 3 | Conversion of ex-US 8 inch Mks 7, 7* &7** |
| Mark 4 | Conversion of ex-US 8 inch Mk 8 or 8½ |
| Mark 5 | Conversion of Mk 1 to suit US 155 mm mounting |
| Mark 5* | Conversion of Mk 1* to suit US 155 mm mounting |
| Mark 6 | New construction, 33 calibres long to suit US 155 mm mounting |
| Mark 6/1 | Mk 6 repaired, body prepared for shrunk in ‘A’ tube |
Data
Marks 1 to 4
| Weight with breech mechanism | 3t 13cwt (Mks 1 & 1*) |
| Total length | 171 inches |
| Length of bore | 161.1 inches (22.4 calibres) |
| Rifling | 40 grooves, uniform Right Hand 1/20 |
| Breech mechanism | Asbury interrupted screw, percussion lock ‘K’ & slide box ‘Y’ |
| Elevation | 0º to +45º (loading angle 7½º) |
| Traverse | 4º right & left |
| Recoil system | Hydropneumatic, variable 24 to 52 inches |
| Weight in action | 22,760 lbs (Mk 3) |
Data
Mark 6
| Weight of gun with breech mechanism | 11,104 lbs |
| Total length | 248 inches |
| Length of bore | 238.1 inches (33 calibres) |
| Rifling | 40 grooves, uniform Right Hand 1/20 |
| Breech mechanism | Asbury interrupted screw, percussion lock ‘K’ & slide box ‘Y’ |
| Elevation | -1º 50′ to +63º |
| Traverse | 30º right & left |
| Recoil system | Hydropneumatic, variable 36 to 60 inches |
| Weight in action | 14.53 tons |
Performance
Marks 1 to 4 firing standard 200 lb HE Shell
| Maximum muzzle velocity | 1,700 feet per second |
| Maximum range | 16,900 yards |
Mark 6 firing standard 200 lb HE Shell
| Maximum muzzle velocity | 1,925 feet per second |
| Maximum range | 19,600 yards |
Ammunition
| Shell, HE, Mark 1D | Streamlined shell filled with Amatol 50/50 & fitted with Fuzes 117, 119 or 231. No time or proximity fuzes ever approved |
| Shell, HE, Mark 2D | The same as the Mk 1D but with 2 driving bands |
| Propelling charge | For Marks 1 – 4 Howitzer a 4 part bag charge was used The Mk 6 used the same plus a single bag charge 5 which replaced the other 4 when used |