The Fairmile B motor launch (often abbreviated to 'ML') was a very numerous class of motor launch produced in kit form by British boatbuilder Fairmile Marine, and then assembled and fitted out by numerous boatyards during the Second World War to meet the Royal Navy's coastal operation requirements.

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.

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.

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.

All boats were essentially the same, although they could be adapted to serve in several roles by the expedient of having pre-drilled rails on their decks spaced to allow the fitting of various types of armaments.

Although their armament initially reflected their main anti-submarine mission, nine of them were fitted with 21-inch (533 mm) torpedo tubes taken from ex-US Town-class destroyers; they formed the 2nd ML Flotilla tasked with anti-invasion duty, until the threat had passed.

[2] A number served in the St Nazaire Raid as assault transports, but their light construction meant that they suffered heavily; 12 B motor launches were lost in the action,[3] out of 16 deployed.

Holt of the Admiralty and built by British boat builder Fairmile Marine, during the Second World War, 88 Fairmile B motor launches, with slight modifications for Canadian climatic and operational conditions, were built in Canada for service with the RCN in home waters.

[7] The first thirty-six Canadian Fairmile B type were designated and painted up as CML 01 to 36 (coastal motor launch).

They were employed on routine patrols, convoy escorts, running special forces in and out of Japanese-held areas, in Papua New Guinea, boom defence patrols in harbours at home and abroad, courier operations, survey work and raiding Japanese-held coasts.

A number of boats were built in Egypt by Thomas Cook & Son, who had a Cairo shipyard for constructing Nile tourist craft.

[13] Post war they were often taken on as pleasure boats and a number of Fairmile Bs are on the National Register of Historic Vessels.