• 
• 
• 

• 

Source: Warplanes of the Third Reich (W. Green)

Dornier's proposal was based broadly on the design of the Do 217 then undergoing prototype trials, the four crew members being housed ahead of the wing in a pressure cabin which, taking the form of a detachable compartment pressurized by tapping the superchargers of the DB 604 engines, was extensively glazed by a series of curved panels. The Technische Amt considered the technically more advanced projects tendered by Focke-Wulf and Junkers more promising than the Do 317, and Dornier was instructed to embody some of the features proposed for its "Bomber B" in a new high-altitude version of the Do 217. Some design development of the Do 317 continued without priority as a possible back-up for the Fw 191 and Ju 288, but after attaining the mock-up stage in 1940, further work was stopped to permit concentration on the Do 217P high-altitude reconnaissance bomber.

In 1941, the Do 317 was resurrected and offered to the RLM as a potential production successor to the Do 217. Two versions were proposed: the simplified and less ambitious Do 317A powered by two DB 603A engines and featuring conventional defensive armament, and the more advanced Do 317B with DB 610 engines, remotely-controlled defensive barbettes, and an extended wing. Six prototypes of the Do 317A were ordered, and the first of these, the Do 317 V1 (VK+IY), commenced its flight test programme in 1943. Following closely the structural design of the Do 217, the Do 317 V1 featured an all-metal two-spar wing carrying slotted ailerons interlinked with electrically-operated split flaps, and accommodating a 343 Imp. gal. fuel tank between the spars on each side of the fuselage, inboard of the engine nacelles, and a 47 Imp. gal. tank immediately outboard of each nacelle. The oval-section fuselage housed a further 462 Imp. gal. of fuel in a main tank immediately aft of the pressure cabin and above the bomb-bay which was designed to accept a maximum load of six 500 kg bombs. The DB 603A 12-cylinder liquid-cooled engines were each rated at 1,750 h.p. for take-off, and although no provision for defensive armament was made in the Do 317 V1, the production Do 317A was to have featured a single 13-mm. MG 131 machine gun in an electrically-operated turret in the roof of the pressure cabin, a fixed forward-firing 15-mm. MG 151 cannon in the lower port side of the forward fuselage, a pair of free-mounted 7.9-mm. MG 81 machine guns projecting from the starboard side of the nose glazing, and two aft-firing 13-mm. MG 131 machine guns on free mountings, one above and the other below the fuselage.

Trials with the Do 317 VI revealed no real performance advance over the Do 217P-0, and the decision was taken, therefore, to complete the remaining five prototypes without cabin pressurization equipment and employ them as Hs 293A missile carriers. In this form the prototypes were redesignated Do 217R, and subsequently saw service with III/KG 100 at Orleans/Bricy. At this time, the Do 317B project had attained the full-scale mock-up stage, but the Technische Amt concluded that it lacked sufficient promise to warrant further development and thus the entire Do 317 prgramme was cancelled. The Do 317B was intended to utilise the same basic airframe as the 317A, but wing span was increased by 17 ft. 7 in. duction of new outer panels, wing fuel tankage w maximum bomb load was raised to 12,346 lb., a armament was intended to consist of a chin barbette housing twin 7.9-mm. MG 81 machine guns, a dorsal barbette containing two 13-mm. MG 131 machine guns, a manned forward turret containing a similar pair of weapons, and a remotely-controlled 20-mm. MG 151 cannon in the extreme tail.