Steam gun boat
Steam gun boats were small Royal Navy vessels built from 1940 to 1942 for Coastal Forces of [World War">British Coastal Forces of World War Two">Coastal Forces of [World War Two|Coastal Forces] during World War II. The class consisted of nine steam-powered torpedo boats combining aspects of both motor torpedo boats and motor gun boats while being twice as large vessels.
They were developed in parallel with the 35-metre long Fairmile D motor torpedo boats, specifically due to the need to hunt down German E-boats at a time of scarcity of suitable diesel engines. While sixty were planned, only an initial batch of nine were ordered on 8 November 1940, of which seven were completed.
Design
The steam gun boats were conceived to answer the seeming need for a craft which was large enough to put to sea in rough weather and which could operate both as a "super-gunboat" and a torpedo carrier, combining the functions of the motor gunboat and motor torpedo boat in the same fashion as did the German E-boats. The Admiralty wanted Denny and Brothers|Denny] to produce a design that was suitable for pre-fabrication construction to enable large numbers to be built.They were the largest of the Coastal Forces vessels, and were the only ones to be built of steel. They resembled a miniature destroyer, and were perhaps the most graceful of all the craft produced during the Second World War. However their comparatively large silhouette was a drawback, making them too easy a target for the faster German craft.
They were long and had a displacement of 172 tons. They were powered by two Metropolitan-Vickers geared steam turbines using special LaMont boilers. These boilers proved to be particularly vulnerable to attack and – once the vessel had broken down – required a major effort to repair. Steam had the advantage of quietness but demanded a large hull. Large wooden hulls were not feasible for mass production, so steel was used. This meant hulls and machinery were beyond the scope of the small yards engaged in the rapid expansion of the coastal forces, and the SGB thus competed for berths in yards already hard put to produce urgently required convoy escorts. Also they competed in the demand for mild steel and steam power plants against the more urgently demanded destroyers; accordingly the planned 51 further vessels were not ordered, and the two units ordered from Thornycroft and Company|Thornycroft] were not completed after air-raid damage. The seven vessels constructed were built by Yarrow, Hawthorn Leslie, J. Samuel White and William Denny and Brothers, entering service by the middle of 1942.
Fuel consumption was heavy. A disadvantage was that, while a petrol boat could start from cold and get away immediately, the SGB had to remain in steam. Over time the addition of 18 mm protective plate over the sides of the boiler and engine rooms, together with the extra armament and crew, increased the displacement to 260 tons and their service speed was consequentially reduced to 30 knots.
Veritable battleships of the coastal forces, the steam gun boats were heavily armed and could maintain high speed in a seaway. In action E-boat commanders respected the SGBs almost as much as destroyers as a single well-placed shot from their three-inch guns could disable or sink an E-boat.
Their armament was arranged with the three-inch gun on the aft deck behind the superstructure, just aft of the torpedo tubes that angled out on either side of the superstructure. There were a pair of six-pounder guns fore and aft, and two twin Oerlikon 20 mm cannons, one in the apex of the bow and one on the stern superfiring over the three-inch gun. Machine guns were mounted in twin mounts on either side of the bridge.
The nearest Kriegsmarine parallel to these were the R boats. Although these 160-ton vessels were designed as minesweepers-minelayers, this class was unique in being equipped with two torpedo tubes and sometimes an 88 mm gun, as well as the typical R boat armament of 37 mm and 20 mm guns and 16 mines. These were usually called "escort minesweepers". However, with a maximum speed of 24 knots they were much slower than the steam gun boats.
Service
A lack of steel and turbines meant that the 52 boats initially planned were reduced to an order of nine boats which received the designations SGB 1 to 9. Numbers 1 and 2 were cancelled when their hulls were badly damaged by an air raid on the Southampton area. The 1st SGB Flotilla was formed at Portsmouth by mid-June 1942, under the command of Lieutenant-Commander Peter Scott. Their first fleet action took place in the Baie de Seine shortly after midnight on 19 June, when two vessels – SGB 7 and 8 – under the joint command of Lieutenant J. D. Ritchie, in company with the Albrighton encountered several E-boats escorting two German merchantmen. SGB 7 was sunk in this action. As a consequence, the Admiralty noted their vulnerability and refitted them with additional armour over their engine and boiler rooms. At the same time the six remaining boats were renamed after wildlife in the form "SGB Grey....".SGB5 was damaged in a fight with German armed trawlers off Berneval while escorting landing craft in the Dieppe Raid August 1942.
1st SGB Flotilla was later based at HMS Aggressive, Newhaven, Sussex on the south coast of England.
In 1944 the six survivors were all converted to fast minesweepers and all except SGB9, Grey Goose, were sold off in the years after the war.
Ships in class
The nine vessels laid down, listed below, were all ordered on 8 November 1940.| Ship | Builder | Laid down | Launched | Commissioned | Fate |
| SGB1 | Thornycroft, Woolston | Cancelled | |||
| SGB2 | Thornycroft, Woolston | Cancelled | |||
| SGB3 Grey Seal | Yarrow, Scotstoun | 24 January 1941 | 29 August 1941 | 21 February 1942 | For sale 20 August 1949 |
| SGB4 Grey Fox | Yarrow, Scotstoun | 24 January 1941 | 25 September 1941 | 15 March 1942 | For sale October 1947 |
| SGB5 Grey Owl | Hawthorn Leslie, Hebburn | 17 April 1941 | 27 August 1941 | 1 April 1942 | Sold to British Iron & Steel Corporation and scrapped 15 December 1949 |
| SGB6 Grey Shark | Hawthorn Leslie, Hebburn | 28 March 1941 | 17 November 1941 | 30 April 1942 | Sold 13 October 1947. Houseboat in 1949 |
| SGB7 | Denny, Dunbarton | 3 February 1941 | 25 September 1941 | 11 March 1942 | Sunk by gunfire from German surface vessels in the Seine Estuary 19 June 1942 |
| SGB8 Grey Wolf | Denny, Dunbarton | 3 February 1941 | 3 November 1941 | 17 April 1942 | Sold 3 February 1948 |
| SGB9 Grey Goose | J. Samuel White, Cowes | 23 January 1941 | 14 February 1942 | 4 July 1942 | Sold about 1957. Converted to houseboat, currently moored at Hoo St Werburgh. |