Flat-iron gunboat

Flat-iron gunboats (more formally known as Rendel gunboats) were a number of classes of coastal gunboats generally characterised by small size, low freeboard, the absence of masts, and the mounting of a single non-traversing large gun, aimed by pointing the vessel. They acquired their nickname from the physical similarity with the flat iron used for ironing clothes during the 19th century.

The first flat-iron gunboat was launched in 1867, and the last in 1894, with the vast majority being built in the years 1870 - 1880. They were designed as a cheap coastal defence weapon, a role they failed to achieve successfully; they found their greatest utility in offensive coastal bombardment. Strongly built, they lasted in some cases into the late 20th century, and saw action in both World Wars. The hull of the British flat-iron Medway lies in shallow water off Bermuda. The Norwegian flat-iron Tyr remains in service under the name Bjorn West, at last report entering Eidsvik shipyard in May 2014 for restoration.

In 1867 Sir W G Armstrong & Company signed an agreement with a local shipbuilder, Dr. Charles Mitchell, whereby Mitchell’s shipyard would build warships and Armstrong’s company would provide the armaments. George Rendel was put in charge of the new venture, and the vessels designed under his leadership were based on a small craft used by the Armstrong factory to test heavy guns. With the assistance of the leading gunnery expert Admiral Sir Astley Cooper-Key, he turned these craft into a gunboat designed for defensive coastal operations.

A typical flat-iron gunboat displaced about 250 tons, had a length of less than 100 feet (30 m) and drew only 6 feet (1.8 m). It was armed with a single large gun (normally 10 to 12 inches, but in the case of the Italian Castore class, a massive 16-inch weapon). The gun, which was mounted at the bow, was designed to be raised and lowered on a hydraulic mechanism so that stability would not be compromised when making sea passages. The gun was aimed by pointing the whole vessel, since the mounting allowed for elevation but not traversing (in the manner of an enormous punt gun). No rigging of any sort was provided, and twin screws were fitted, allowing for a much reduced draught while at the same time making them highly manoeuvrable. Top speed would have been less than 9 knots (17 km/h), but they were designed to be towed at considerably higher speeds than they were capable of making under their own power. The crew would have numbered about 30 men. Larger variations were built, with the German Wespe class displacing as much as 1,157 tons. Masted versions were produced, particularly for navies with inadequate coaling facilities and long coastlines, and commensurate with an increase in displacement, armament and rigging, crews increased to match, with the Wespe class needing 76 men.

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