Blockship

[1][2][3] The above is the principal and enduring meaning of 'block ship', but in the mid-19th century the term blockships was applied to two groups of mobile sea batteries developed by the Royal Commission on Coast Defence.

The first batch of four was obtained from around 1845 by converting old sailing 74-gun two-deckers, all of them Vengeur-class ships of the line, into floating batteries, equipped with a steam/screw propulsion system.

Also called "steam guardships",[4] these conversions involved cutting down to a single deck, with ballast removed, and a jury rig installed with a medium 450-horsepower (340 kW) engine for speeds of 5.8–8.9 knots (10.7–16.5 km/h; 6.7–10.2 mph).

Although these ships were intended for coast defence some of them were used offensively, notably in the Baltic Campaign of 1854 and 1855, where they were an integral part of the British fleet.

A second batch of five were similarly obtained from around 1855 by converting other elderly 74-gun ships; these were Russell, Cornwallis, Hawke, Pembroke and Hastings.