1:300 Fairmile "D", with it's two single 6 pdr., 4 18" tubes and twin 20mm © Andrew Arthur

When the limits of the 60 / 70 foot hulls became apparent, the 110 / 113 foot hull was the larger standard, and with far more space for armament and power to be worked in, large, fast and heavily armed MGB's or MTB's could be built. It was also realised that by adding 2 or 4 torpedo tubes to the large MGB hulls, without losing any of the armament, a capable dual-purpose design could be evolved, and with two 6 pound ( 57mm ) guns, they were far more capable than the single 37mm Flak of the "E" boats.
Those boats with the MGB prefix were later renamed MTB.

1:300 Modified "D" had 2 x 21" tubes and rocket launchers © Andrew Arthur

A standard "D" hull, but with greater displacement, the main difference was the replacement of the 4 x 18" torpedoes with 2 x 21" type. Also, for shore bombardment and night illumination, 1 or 2 RAF type rocket launchers were fitted.
17 were converted to RAF Rescue & Safety craft post war.