Fairmile D: the heavily armed ambush boat

The Fairmile D was a major program: 229 boats were planned and 228 completed. It did not have a single immutable armament, because the nominal pair of six-pounder 57 mm guns, 20 mm cannon, machine guns, depth charges, smoke gear, and searchlight formed only a starting point for crew modifications. The design's firepower was respected enough that the Kriegsmarine placed two captured examples in service. Its quoted 29-knot top speed was much lower than a Schnellboot's roughly 44 knots, but radar and radio interception could position the gunboats ahead of German formations. Torpedo boats sent against Britain's east-coast convoys could then be caught at close range before reaching the convoy screen. In this role, the Fairmile D became an ambush predator intended to stop attackers before they reached merchant traffic.