5.5 inch Ordnance BL Medium Gun

5.5 inch Ordnance, breech loading 5.5 inch medium gun. The barrel is mounted on a two wheeled carriage with split trails. The spades on the trail are located on the top of each trail while in the travelling position. The barrel is made from ordnance steel and has no muzzle brake. The trunnions on the cradle are towards the rear, allowing recoil at full elevation. To compensate for the barrel mass being so far forward, two equilibrators are mounted vertically in front of the trunnions, bearing on the cradle. The breech mechanism of the gun is based on a modified interrupted screw type Welin breech design combined with the Asbury operating mechanism.

The gun is painted a semi gloss olive drab colour. Markings - 1-14-1-10 (YELLOW PHOENIX). This gun has the 1st Division tactical sign, 8/12th Medium Regiment, 103rd Medium Battery formation signs. AMF registration number 05018. A complete equipment schedule is provided.

The 5.5 inch gun was a contemporary of the 25 pounder, entering service in May 1942. It saw a great deal of service during the Second World War with British and Canadian forces, throughout the later part of the Western Desert campaign in the Italian campaign and in the European theatre. Guns with the 21st Army Group fired over 2.6 million rounds between 'D' day and VE day.

In Australian service the gun did not see service outside of Australia. The gun was designed to be towed by a Leyland 10-ton tractor which gave it good cross country mobility and allowed it to be brought into action by its 10 man crew in 3 to 5 minutes.

The split trail allowed the detachment to load the heavy shells with ease, but also gave the gun an excellent top traverse of 30 degrees left and right.

The breech mechanism of the gun is based on a modified Welin breech screw design combined with the Asbury mechanism which was introduced in 1916. This system gives excellent strength and reliability, and although the ammunition is of a separate loading, bag charge variety, the gun had a fairly high rate of fire. The gun also employs a quick loading device which enables the detachment to swing the barrel down to a loading angle and return to its original elevation after loading, with minimum effort and maximum speed.

Average shell weights varied from 37.2kg (82 lb) to 45.4kg (100 lb). Range with the 82lb shell was 18000 yards, and with the 100lb shell as 16000 yards.

• 5.5 inch Ordnance BL Field Gun Tool Box