C.Andrews Vickers Aircraft since 1908 (Putnam)

<...>
Before leaving the experimental Vickers aircraft of the first world war, mention must be made of the continuance of the buried-engine idea in the projected F.B.15, with two Rolls-Royce engines mounted in the fuselage and driving two outboard propellers via shafting and gearing. All these projects were stillborn because of the difficulty of engineering the gearing at that time. The span of the F.B.15 was to have been 80 ft and the length 46 ft; construction of two prototypes was started but soon abandoned.
A smaller aircraft, again with buried engines, reached an advanced stage of construction before being abandoned, most probably for the reason already stated in connection with the gearing. This was the triplane F.T.2 (see drawing on page 482), intended to take two 200 hp Lorraines, with a designed speed of 124 mph and a weight of 2,055 lb as compared with the estimated weight of 3,700 lb for the F.B.15.
These projects were based on the battleplane philosophy of air combat; that is, a large aeroplane bristling with armament covering all blind spots, but in reality easy meat to the highly manoeuvrable fighters of that era. Between the wars ungainly French aircraft of this class, called multiplaces de combat, did emerge, but not until the second world war was the idea ever realised in battle, when the high-flying massed formations of American heavily armed decoy bombers fought in daylight against the Luftwaffe.