1:300 Fairmile "A", with an early war armament of two twin and one single 0.303" MG and a single 3 pounder © Andrew Arthur

Ordered on the eve of the war, the Fairmile "A" was based on the long rounded bilge 110 foot hull. It was a generla purpose armed boat, not as fast or powerful as an MGB, and better suited for local defence, patrol and gunboat duties, as well as river and esturial work. They differed from all the other fast motor boats in that they had a very obvious and sizeable funnel, abaft the standard style of wheelhouse.
The main gun, a 2 or 3 pounder, was mounted aft, where it was dry in heavy seas, but lacked for'ard arcs of fire. 5 light MG's made up the rest of the guns, and 12 depth charges could be carried.
Being supercede by the far more capable and utilitarian Fairmile "B", they were converted to minelayers or other light craft.

1:300 Fairmile "B", showing main gun moved forward, and the 20mm AA aft. The bridge was also moved farther aft © Andrew Arthur

Basically a re-arranged "A" type, on the longer 112~3 foot hull, the "B" lacked one engine and shaft to ease supply problems, and shed 5 knots in doing so. Conversely, over twice as much fuel could be carried, so range increased hugely.
The main gun, a Bofors or a 3 pounder was mounted ahead, for better arcs of fire, and the wheelhouse moved aft to compensate. Two twin 0.303" MG remained in the wings, and a single 20mm AA was mounted abaft the funnel. Where previously the main gun was, a powered twin 20mm mounting was in lieu.
They completely dwarfed the preceding class in terms of numbers built.