Steam Gun Boat

Steam gun boat (SGB) was a Royal Navy term for a class of small naval vessels used during the Second World War. The class consisted of nine gun boats, powered by steam, and built from 1940 to 1942 for the Coastal Forces of the Royal Navy.

They were developed in parallel with the Fairmile D motor torpedo boats ("dog boats"), specifically as a response to the need to hunt down German E-boats and also as a response to the 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.

Grey Goose FL4607
Grey Goose
Class overview
Name: Steam gun boat (SGB)
Operators: RN
Built: 1940-1942
In service: Nov 1941- post-war
Completed: 7
Active: none
Lost: 1
General characteristics
Displacement: 175 tons (standard), 255 tons (deep load)
Length: 44.3 m (145 ft 8 in) overall
Beam: 7.1 m (20 ft)
Draught: 1.68 m (5 ft 6 in)
Installed power: 8,000 shp (5,965 kW)
Speed: 35 kn (65 km/h) maximum
  • 200 NM (370 km) at full speed
  • 900 NM (1,700 km) at 12 knots
Complement: 27 initially (3 officers and 24 men), later rising to 34 as a result of changes in armament


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 Gun Boat (MGB) and Motor Torpedo Boat (MTB) in the same fashion as did the German E-boats. The Admiralty wanted Denny to produce a design that was suitable for pre-fabrication construction to enable large numbers to be built.[1]

They were the largest of the Coastal Forces vessels, and were the only ones to be built of steel (to meet the fast production requirement — all other Coastal Forces craft were of wood). 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 145 ft 8 in (44.40 m) long and had a displacement of 172 tons (202 tons fully fueled). They were powered by two 4,000 hp steam turbines using special flash 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 never ordered, while the two units ordered from Thornycroft were never begun due to enemy action. The seven vessels actually completed 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 with the added disadvantage 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 (0.7 in) 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, since like destroyers, a single well-placed shot from their 3-inch gun could disable or sink an E-boat.

Their armament arrangement had 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 (57 mm) 6-pounder guns fore and aft, and two twin Oerlikon 20mm cannons, one in the apex of the bow and one on the stern superfiring over the 3-inch gun. Machine guns in twin mounts on either side of the bridge completed the set-up.

The nearest Kriegsmarine parallel to these was the R-301 class of 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 88mm gun, as well as the typical R boat armament of 37mm and 20mm guns and 16 mines. These were usually called "Escort minesweepers". They were slightly slower than the Steam Gun Boats, however.


A lack of steel and turbines meant that the 52 boats initially planned was 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.[2] The 1st SGB Flotilla was formed at Portsmouth by mid-June 1942, under the command of Lieutenant-Commander Peter Scott, son of the Antarctic explorer Captain Robert Scott, later a noted ornithologist, conservationist and broadcaster. Their first fleet action took place in the Baie de Seine (the estuary of the Seine River) 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 Hunt-class destroyer 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 the additional armour over their engine and boiler rooms. At the same time the six survivors were renamed after wildlife in the form "SGB Grey....".[3]

Grey Owl was damaged in a fight with German armed trawlers off Berneval while escorting landing craft in the Dieppe Raid August 1942.

Motor Gun Boats during the Second World War, 1939-1945 HU105409

Grey Goose SGB9
captained by the flotilla commander Peter Scott

Grey Shark FL5161

Grey Shark FL5161

Grey Seal FL5168 (cropped)

Grey Seal FL5168

Grey Fox FL4636

Grey Fox FL4636

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
Grey Seal
Yarrow, Scotstoun 24 January 1941 29 August 1941 21 February 1942 For sale 20 August 1949
Grey Fox
Yarrow, Scotstoun 24 January 1941 25 September 1941 15 March 1942 For sale October 1947
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
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
Grey Wolf
Denny, Dunbarton 3 February 1941 3 November 1941 17 April 1942 Sold 3 February 1948
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.

These boats formed the 1st SGB Flotilla which was initially formed at Portsmouth, but later based at HMS Aggressive, Newhaven, Sussex on the south coast of England.

SGB 5 was damaged in the Dieppe raid after meeting a German convoy of R boats. 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.

SGB9 remained in service as a propulsion trials vessel from 1952 to 1956, her steam engines replaced by Vospers with a pair of experimental Rolls-Royce RM60 marine gas turbines and becoming the first vessel to rely solely on gas turbines for propulsion.[4] The highly advanced turbines featured intercooled compressors and recuperators to boost turbine power output and reduce fuel consumption. Over the original steam machinery, the gas turbine powerplant provided 35% more power while weighing 50% less and using 25% less space.[5] Although the experimental powerplant proved very successful, it was too complex and supporting technology too immature for wider service at that time and SGB9 was placed in reserve at the end of the trials in 1957.[6] With the experimental engines removed SGB9 was sold off in 1958, becoming a mercantile repair hulk. Sold in 1984, the hulk was converted to a houseboat and renamed Anserava. She is currently moored on the River Medway near Hoo St Werburgh in Kent, England.



  1. ^ Konstam (2010) p19
  2. ^ Konstam (2010) p19-20
  3. ^ BBC WW2 Peoples War Archived 1 December 2009 at the Wayback Machine accessed 11 December 2007
  4. ^ Walsh, Philip P.; Paul Fletcher (2004). Gas Turbine Performance (2nd ed.). John Wiley and Sons. p. 25. ISBN 978-0-632-06434-2.
  5. ^ Ellacott, Samuel Ernest (1958). The story of ships (2nd (Hardcover) ed.). UK: Methuen & Co. p. 78. ISBN 978-0-416-54210-3.
  6. ^ Harmon, Robert A. (May 1990). "Marine Gas Turbines: A New Generation". Mechanical Engineering-CIME. American Society of Mechanical Engineers.


External links

Amenities ship

An amenities ship is a ship outfitted with recreational facilities as part of a mobile naval base. Amenities ships included movie theaters and canteens staffed by mercantile crews of the Royal Fleet Auxiliary service. These ships were intended to provide a place where British Pacific Fleet personnel could relax between operations.

Ammunition ship

An ammunition ship is an auxiliary ship specially configured to carry ammunition, usually for naval ships and aircraft. An ammunition ship′s cargo handling systems, designed with extreme safety in mind, include ammunition hoists with airlocks between decks, and mechanisms for flooding entire compartments with sea water in case of emergencies. Ammunition ships most often deliver their cargo to other ships using underway replenishment, using both connected replenishment and vertical replenishment. To a lesser extent, they transport ammunition from one shore-based weapons station to another.

Coastal minesweeper

Coastal minesweeper is a term used by the United States Navy to indicate a minesweeper intended for coastal use as opposed to participating in fleet operations at sea.

Because of its small size—usually less than 100 feet in length—and construction—wood as opposed to steel—and slow speed—usually about 9 or 10 knots—the coastal minesweeper was considered too fragile and slow to operate on the high seas with the fleet.

Minesweeping, in conjunction with fleet activities, was usually relegated to the diesel-driven steel-hulled AM-type minesweepers, later to be replaced by the wood-hulled MSO-type minesweeper with aluminum engines.

Coastal submarine

A coastal submarine or littoral submarine is a small, maneuverable submarine with shallow draft well suited to navigation of coastal channels and harbors. Although size is not precisely defined, coastal submarines are larger than midget submarines, but smaller than sea-going submarines designed for longer patrols on the open ocean. Space limitations aboard coastal submarines restrict fuel availability for distant travel, food availability for extended patrol duration, and number of weapons carried. Within those limitations, however, coastal submarines may be able to reach areas inaccessible to larger submarines, and be more difficult to detect.

Combat stores ship

Combat stores ships, or storeships, were originally a designation given to ships in the Age of Sail and immediately afterward that navies used to stow supplies and other goods for naval purposes. Today, the United States Navy and the Royal Navy operate modern combat store ships. The Sirius and Mars classes (for the US) and the Fort Rosalie and Fort Victoria classes (for the UK) provide supplies, including frozen, chilled and dry provisions, and propulsion and aviation fuel to combatant ships that are at sea for extended periods of time. Storeships should not be confused with fast combat support ships or tenders.

Destroyer tender

A destroyer tender, or destroyer depot ship in British English, is an auxiliary ship designed to provide maintenance support to a flotilla of destroyers or other small warships. The use of this class has faded from its peak in the first half of the 20th century as the roles of small combatants have evolved (in conjunction with technological advances in propulsion reliability and efficiency).

General stores issue ship

General stores issue ship is a type of ship used by the United States Navy during World War II and for some time afterwards.

The task of the general stores issue ship was to sail into non-combat, or rear, areas and disburse general stores, such as canned goods, toilet paper, office supplies, etc., to ships and stations.

Guard ship

A guard ship is a warship assigned as a stationary guard in a port or harbour, as opposed to a coastal patrol boat which serves its protective role at sea.

HMS Aggressive (shore establishment)

HMS Aggressive was a shore establishment of the British Royal Navy during World War II, based at Newhaven, East Sussex.

Light aircraft carrier

A light aircraft carrier, or light fleet carrier, is an aircraft carrier that is smaller than the standard carriers of a navy. The precise definition of the type varies by country; light carriers typically have a complement of aircraft only one-half to two-thirds the size of a full-sized fleet carrier. A light carrier was similar in concept to an escort carrier in most respects, however light carriers were intended for higher speeds to be deployed alongside fleet carriers, while escort carriers usually defended convoys and provided air support during amphibious operations.

Merchant raider

Merchant raiders are armed commerce raiding ships that disguise themselves as non-combatant merchant vessels.

Mine countermeasures vessel

A mine countermeasures vessel or MCMV is a type of naval ship designed for the location of and destruction of naval mines which combines the role of a minesweeper and minehunter in one hull. The term MCMV is also applied collectively to minehunters and minesweepers.


A minehunter is a naval vessel that seeks, detects, and destroys individual naval mines. Minesweepers, on the other hand, clear mined areas as a whole, without prior detection of mines. A vessel that combines both of these roles is known as a mine countermeasures vessel (MCMV).

Motor Gun Boat

Motor Gun Boat (MGB) was a Royal Navy term for a small military vessel of the Second World War. Such boats were physically similar to Motor Torpedo Boats (MTBs), equipped instead with a mix of guns instead of torpedoes. Their small size and high speed made them difficult targets for E-boats or torpedo bombers, but they were particularly vulnerable to mines and heavy weather. The large number of guns meant the crew was relatively large, numbering as high as thirty men.

Net laying ship

A net laying ship, also known as a net layer, net tender, gate ship or boom defence vessel was a type of small auxiliary ship.

A net layer's primary function was to lay and maintain steel anti-torpedo or anti-submarine nets. Nets could be laid around an individual ship at anchor, or around harbors or other anchorages. Net laying was potentially dangerous work, and net laying seamen were experts at dealing with blocks, tackles, knots and splicing. As World War II progressed, net layers were pressed into a variety of additional roles including salvage, troop and cargo transport, buoy maintenance, and service as tugboats.

Ocean boarding vessel

Ocean boarding vessels (OBVs) were merchant ships taken over by the Royal Navy for the purpose of enforcing wartime blockades by intercepting and boarding foreign vessels.

Repair ship

A repair ship is a naval auxiliary ship designed to provide maintenance support to warships. Repair ships provide similar services to destroyer, submarine and seaplane tenders or depot ships, but may offer a broader range of repair capability including equipment and personnel for repair of more significant machinery failures or battle damage.


SGB may refer to:

BanksASX code for St. George Bank, an Australian bank

Société Générale de Belgique, Belgian bankEntertainment and mediaSuper Game Boy, a Super Nintendo Entertainment System accessory

Russian Spetsnaz Guards Brigade, a faction in the Tom Clancy's EndWar video game and novelizationLawSozialgesetzbuch, the German Code of social lawMedicalStellate ganglion block, an anesthetic injection in the stellate ganglionOtherA measure of latitude in the Supergalactic coordinate system

Scholengemeenschap Bonaire, the secondary school on that island

Schweizerischer Gewerkschaftsbund, the Swiss Trade Union Confederation

Steam Gun Boat, World War II Royal Navy vessels

Speedway Great Britain, comprising two divisions:

SGB Premiership

SGB Championship

Submarine tender

A submarine tender is a type of depot ship that supplies and supports submarines.

Aircraft carriers
Patrol craft
Fast attack craft
Mine warfare
Command and support


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