Marks I–IV

The 8-inch barrels were re-lined to 7.2 inches (183 mm) and the old carriages were retained although the original steel rimmed wheels were replaced with new pneumatic balloon-tyre wheels, as was consistent with the motorisation of the British Army. The new four-charge ammunition increased the range to 16,900 yd (15,500 m), but when fired at full charge the recoil caused the weapon to rear violently and jump backwards. To help counter this, two wedge shaped ramps were placed behind the wheels although the gun could sometimes still jump over them, presenting a hazard to crews. Marks I–IV differed only in the original 8-inch barrel used and the type of conversion; some barrels and carriages were also supplied from US First World War stocks.^[1][2][5]

Mark V

In 1944 several 7.2-inch barrels were placed in the US Carriage M1 used by the 155 mm Long Tom already in use by the British Army, becoming the BL 7.2-inch howitzer Mk V. Few Mk Vs were produced and it was never issued to batteries, as it was apparent that the Carriage M1 was capable of accepting greater recoil forces.^[1][2]

Mark 6

The BL 7.2-inch howitzer Mk 6 (there was a shift from Roman numerals) retained the Carriage M1 of the Mk V but had a new built 7.2-inch 6 ft 5 in (1.96 m) longer barrel than previous marks, additionally a fifth charge was added to the ammunition. The longer barrel and extra charge provided an increase in range to 19,600 yd (17,900 m),^[6] and the new carriage also provided a far more stable platform, greatly increasing accuracy. The Mk 6 was considered a highly effective gun and it was retained in service after the war.^[1][2]

Indian Army service

In 1957, Indian Army raised 60 Heavy Regiment from the erstwhile J&K Bodyguard Cavalry. The unit was unique in its composition of four batteries with four Mk 6 BL 7.2-inch Howitzers in each battery, unlike the standard three-battery (six guns each) composition of other Indian artillery regiments. The guns of 60 Heavy Regiment saw combat in the 1965 and 1971 wars against Pakistan. In the early 1990s 60 Heavy Regiment was converted to a field regiment and the guns were passed on to 61 Heavy Regiment. They were finally retired from service by the late 1990s.

User units

 Newfoundland^[3]

• 59 (Newfoundland) Heavy Regiment

 United Kingdom (Royal Artillery)^[3][9][10]

• 1 Heavy Regiment
• 32 Heavy Regiment
• 51 (Lowland) Heavy Regiment – North West Europe Campaign
• 52 (Bedfordshire Yeomanry) Heavy Regiment – North West Europe Campaign
• 53 Heavy Regiment
• 54 Heavy Regiment
• 55 Heavy Regiment
• 56 Heavy Regiment – Mediterranean Theatre and North West Europe Campaign
• 58 Heavy Regiment
• 60 Heavy Regiment
• 61 Heavy Regiment
• 75 Heavy Regiment
• 171 Heavy Regiment
• 114th (Sussex) Field Regiment – 2 gun section during Burma Campaign
• 8th (Belfast) Heavy Anti-Aircraft Regiment – 2 gun section during Burma Campaign
• 52nd (London) Heavy Anti-Aircraft Regiment – 2 gun section during Burma Campaign
• 56th (Cornwall) Heavy Anti-Aircraft Regiment – 2 gun section during Burma Campaign
• 67th (York and Lancaster Regiment) Heavy Anti-Aircraft Regiment – 2 gun section during Burma Campaign
• 101st Heavy Anti-Aircraft Regiment – 2 gun section during Burma Campaign

 India (Regiment of Artillery)^{[citation needed]}

• 143 Heavy Regiment Artillery (TA) (1951-1957)
• 60 Heavy Regiment (now 60 Medium Regiment) (1957-1991)
  • 128 Hy Bty
  • 129 Hy Bty
  • 130 Hy Bty
  • 131 Hy Bty (later transferred to 106 Med Regt after one gun was put out of action)
• 61 Heavy Regiment (1991-1996)