Displacement :90t
Dimensions :Length :33.53 m Width :6.40 m Draught :1.58
Drive :4 gasoline engines developing 5,000 hp and driving 4 shafts.
Speed :29 knots
Armament(s)...
2 single '6' guns, 1 twin
20 mm cannon, 2 twin 12.7 mm machine guns and (optional)
4 457 torpedoes mm.
Crew: up to 30 officers and sailors.
The British knew from before the war that the MTBs, before reaching an objective, would probably have difficulty breaking through the defense of a resolute escort, especially if this escort consisted of S-Boote. For this type of operation, the Royal Navy therefore needed a more powerfully armed, yet fast, boat to divert the attention of the German launches, defend the MTBs and allow them to concentrate on their main target. It also needed a boat capable of protecting convoys against S-boats in the absence of a destroyer escort. As mentioned above, some of the available Masby BPBs were rearmed to temporarily perform this support function, but longer term projects led to the development of the Fairmile D and the steam gunboat.
Half the length of the standard MTB, the D class had an unusual shell:V-shaped and rather flat at the back, it rounded at the front, the transition between these two parts taking the form of a pronounced ridge which played a useful role against splashing water. Thanks to this hybrid hull and the increase in their length, the Fairmile Ds could operate in rougher seas without being too roughed up. The ardor of the transom allowed the installation of a propulsion system with four shafts; the smaller diameter propellers reduced the draft, but this characteristic was more due to the power of the engines available than to construction requirements. The first units were direct drive, but a gearbox was fitted later, which improved both efficiency and speed. The difficult conditions in which these buildings were deployed highlighted the weaknesses of mass production applied to a wooden model of this size, and the approximately two hundred Fairmile Ds which were produced between 1942 and 1944 had to be subject to frequent repairs and consolidations. The armament, official or not, varied a lot, these boats being used as MGB (90 t of displace' MTB (95 t) or MGB/MTB (1( In this last form, they seduced an impressive power.