The Fairmile B motor launch (often abbreviated to 'ML') was a large class of motor launch built by British boatbuilder Fairmile Marine and others during the Second World War to meet the Royal Navy's coastal operation requirements.
Design
While the Type A motor launch had been designed entirely by Fairmile, the Type B design had come from Bill Holt, head of the Admiralty's DNC Boat Section. The hard-chine hull of the Type A had exhibited seakeeping and handling limitations, but Holt's round-bilged design for the Type B was a far more seaworthy form.
Like all Fairmile boats, production of the Type B was based on total prefabrication so individual components could be contracted out to small factories for production and these arranged as kits that would be delivered in stages to various boatyards for assembly & fitting out on a 'just-in-time' basis. Accordingly, the detailed design work for the Type B was taken on by Fairmile and modified to suit their kit fabrication principle - they then also handled production of component parts.
Altogether approximately 650 boats were built between 1940 and 1945. Like the Type As, the Type Bs were initially intended as submarine chasers, so the boats were fitted with ASDIC (sonar) as standard.
Their main armament initially reflected their anti-submarine focus, with 12 depth charges, a single QF 3-pounder Hotchkiss gun forward, and one set of twin 0.303-in Lewis or GO machine guns (frequently increased in number by the crew); early boats often received a Holman projector amidships. A common upgrade to gun armament by 1942-43 in many early boats was to add an aft bandstand mounting for either a 2-pdr Rolls gun or a 20mm Oerlikon cannon. The specifications given are for the original 1940 British version.
As the war moved on, the vessels were adapted to other roles and the armament was modified and upgraded such as the replacement of the 3-pounder with one or more 20 mm Oerlikon cannon and removal of the ASDIC dome for more clearance as minesweepers. Some boats were configured as motor torpedo boats.
Boats
The Fairmile B type superseded the original Fairmile A type, which had been designed designed by Normman Hart. An initial batch of 24 of these (ML 101 to ML 124) was ordered by the Admiralty on 22 September 1939 from the Fairmile Marine company, of which the first eleven (plus the prototype ML 100) were completed to the Hart design; the remaining thirteen (ML 112 to ML 124) were completed to the Fairmile B design. The first Fairmile B motor launch (actually ML 113 from Tough Bros, Teddington) was completed and delivered on 12 August 1940, with a further eleven from this first production batch entering service before the end of the year (the last of the batch to be completed - ML 123 - was delayed until 1941).
The Admiralty placed a massive order for a second batch of Fairmile Bs - 120 in total - on 8 January 1940. These were numbered ML 125 to ML 244. Of these, 37 were delivered by the end of 1940 and the other 83 during the first half of 1941. A third batch, this time of 65 boats, was placed on 21 May 1940; these were numbered ML 245 to ML 309, and were all delivered during 1941, as were two extra units (ML 310 and ML 311) ordered on 28 June 1940 for Singapore to be assembled by the Singapore Harbour Board; this last pair were delivered to Singapore on 29 November 1941, only to be lost in February 1942 to the Japanese (who re-used ML 310 under the name Suikei 12).
The fourth batch of 24 boats was ordered on 28 July 1940 as ML 312 to ML 335. However, these were altered to be completed instead as Motor Gunboats, and the prefixes to their numbers changed from "ML" to "MGB", retaining the same numbers. In their place, a new batch of 50 Fairmile Bs was ordered on 21 August, and these became ML 336 to ML 367 (the last six of these for assembly by the Singapore Harbour Board) and ML 372 to ML 389. Six days later another 6 were ordered, ML 368 and ML 369 for the Royal Canadian Navy, ML 370 and ML 371 for assembly in Jamaica for Caribbean service, and ML 390 and ML 391 intended for assembly at Singapore, although this last pair was switched to Bombay Dockyard on 22 February 1942 following the fall of Singapore. Further batches followed, producing ML 392 onwards, mainly in Overseas yards, with a final total of about 650 boats of this Type eventually assembly worldwide, including 60 in Canada.