RBL 20 pounder Armstrong gun

• Name — RBL 20-pounder gun • Origin — United Kingdom • Type — Naval gun Field gun • Is Ranged — yes • Is Artillery — yes • Is Uk — yes • Service — 1859 – 19?? • Used By — British Empire • Designer — W.G. Armstrong Co. • Number — 412 • Variants — 13, 15 and 16 cwt • Weight — Naval: 13 long cwt or 15 long cwt Field: 16 long cwt • Part Length — Naval: 54 in Field: 84 in bore & chamber • Caliber — 3.75 in • Cartridge — 21 lb • Velocity — Naval: 1000 ft/s Field: 1130 ft/s • Range — 3400 yd • Breech — Armstrong screw with vertical sliding vent-piece (block)

The gun was effectively a larger version of the successful RBL 12 pounder 8 cwt Armstrong gun. There were different versions for land and sea service.

• Illustration — 13 cwt boat gun at Hong Kong Museum of Coastal Defence The RBL 20 pounder of 13 cwt and 15 cwt for sea service was introduced in 1859. It is 2½ feet shorter than the land version giving it a bore of only 54 inches (14.43 calibres), and hence a short stubby appearance. Its short barrel only allowed it to attain a muzzle velocity of 1,000 ft/second. The 15 cwt gun, identifiable by the raised coil in front of the vent slot, was intended for broadside use in sloops. The more lightly constructed 13 cwt gun was known as a pinnace gun and was intended for boat use.

The RBL 20 pounder of 16 cwt for land service was introduced in 1860. It has a bore of 84 inches (22.36 calibres) and hence has the appearance of a typical field gun. After it became obsolete for regular Royal Artillery use, a small number were re-issued to Volunteer Artillery Batteries of Position from 1889, alongside 16-pounder RML guns and 40 Pounder RBL guns. The 1893 the War Office Mobilisation Scheme shows the allocation of twelve Artillery Volunteer position batteries equipped with 20 Pounder guns which would be concentrated in Epping, Essex in the event of mobilisation.

• An unrestored 13 cwt pinnace gun at Hong Kong Museum of Coastal Defence • A 16 cwt gun on board HMS Warrior at Portsmouth, UK • A 13 cwt gun dated 1859 at the Artillery Museum, North Head, Sydney, Australia • Sea Service Pattern at Explosion! Museum of Naval Firepower, Gosport