BL 4 inch Mk I – VI gun

• Name — Ordnance BL 4-inch gun Mk I – Mk VI • Origin — United Kingdom • Type — Naval gun • Is Ranged — yes • Is Artillery — yes • Is Uk — yes • Service — 1880s – 190? • Used By — United Kingdom • Part Length — Mk I 22.5cwt: 100 in bore (25 calibres) Mk II – VI: 108 in bore (27 calibres) 120 inches total • Cartridge — 25 lb • Caliber — 4 in • Velocity — Mk I 13cwt: 1180 ft/s Mk II – VI: 1900 ft/s • Max Range — Mk II-VI 7700 yd • Breech — 3-motion screw

This was the first 4-inch BL gun. With its short (60-inch total) barrel it had a range of only 5,500 yards.

With its longer barrel (100 inch bore) Mk I had a range of 7,200 yards. Both early Mk I types were quickly withdrawn from service following the explosion of a similar BL 6 inch Mk II gun on board HMS Cordelia in June 1891. Mk I 22.5 cwt continued to be used for training.

The improved 27-calibre Mk II gun and subsequent Marks, often referred to as 4 inch 26 cwt, replaced the early Mk I versions in service. The longer barrel (108 inch bore: 27 calibres) gave it a range of 7,700 yards. Mk II guns and later Marks armed the following warships: • Inflexible as re-gunned in 1885 • Bellerophon as re-gunned in 1885 • Pygmy-class composite screw gunboats of 1888 • s launched in 1889 • Alexandra as re-gunned in 1891 • s of 1894 The gun was succeeded in its class from 1895 by the QF 4-inch gun Mk I.

A small number of these guns were converted to QF to use the same cartridges as the QF 4-inch gun. They were designated Mk I/IV, I/VI etc. depending on which Mark of BL 4-inch had been converted. All had a bore of 27.85 calibres after conversion, with a muzzle velocity of 2,177 ft/second.

• A gun from 1888 at Explosion! The Museum of Naval Firepower, Gosport from Victorian Forts and Artillery website • A gun from HMS Gannet, mounted on top of Calshot Castle at the entrance to Southampton Water from Victorian Forts and Artillery website