36 Regiment Royal Artillery​

The 3.7 was introduced in 1937, fortunately allowing enough time for production to

get under way before the outbreak of World War 2. It fired a 28-lb (12.72 kg) shell

to a ceiling of 32,000 feet (9754 m), a significant improvement on the 3-inch.

 

During the war an automatic fuze-setter (MFS No 11) and an automatic loader were fitted.

These not only speeded up the rate of fire, but by eliminating variations in time taken by individuals

 in loading and fuze-setting, enabled guns to follow data supplied by predictor more closely.

 

Thus the new machinery not only increased the rate of fire from 10 to 20 rpm, but also

 improved accuracy. Guns so equipped were designated Mark 3A.

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But as World War 2 progressed, and bombers flew ever higher, still more effective equipment

was demanded to cope with them. Experiments with a proposed 4.7-inch gun were not

successful so in 1941 a number of Naval QF 4.5-in guns were obtained, the barrels lined down

to 3.7, but the original chamber retained so that a 4.5 cartridge could be fired. This combination

sent the same 28-lb shell to 45,000 feet (13,776 metres).

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To increase the performance of the 4.5/3.7 combination Colonel Probert of the Research

Department, Woolwich Arsenal, developed a special barrel in which the rifling gradually

decreased in depth from the breech to five calibres from the muzzle where it disappeared

altogether and the barrel became smooth-bored. In addition to a heavier driving band the

 projectile was fitted with 'steadying bands' near the shoulder. The smooth-bore section of

the barrel swaged down the driving and steadying bands flush with the surface of the shell,

thus improving its ballistic qualities.

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In the latter stages of World War 2 the Allies enjoyed air superiority, so a number of 3.7 guns

were converted to fire. in the field role in which they performed satisfactorily - where crest

clearance was no problem. The late WO1(SMIG) JT (Terry) Transom converted a 3.7 at the

School of Artillery in 1956. A QF 4.5-in howitzer sight-supporting pintle was welded to

the top of the traversing gear column, and on the pintle was attached a 4.5 sight bracket

with a dial sight. On the elevation side of the gun a sight clinometer was attached to

 indicate elevation. The combination worked very well but unfortunately the fire of

1957 which destroyed the 4.5 sight brackets ended further practice.