The RFC AVRO 504A
(Monochrome Photograph - Taken At a War Office Conference held on April 20, 1915 A.V. Roe agreed to make 29 design changes to the 504s for future supply to the RFC and to give the subsequent machines the revised designation of Avro 504A. The most conspicuous of these changes was the reduction in the span (area) of the wing ailerons making the aeroplane less sensitive to control in roll.)
The RNAS AVRO 504B
(Monochrome Photograph - Showing the second production Avro 504B at the RNAS training airfield Chingford 1915.)
At the outbreak of war the RNAS also ordered 50 Avro 504s (RNAS Nos 1001-1050) and with the perceived success of the Friedrichshafen Raid they requested changes to the original design from Avro during production.
The first change, from 1029 onward, was to replace the original
'comma' shaped balanced rudder with a fixed fin and unbalanced type.
The second change, from 1043, was to provide a cut-out on each side of the pilot's rear cockpit to enable him to lean out and look down at the ground though an externally mounted bomb sight. This version
became the Avro 504B.
The RNAS AVRO 504C
The next variant, the 504C, was effectively a production version of the special long range Friedrichshafen bombing machines. These were single seat aircraft with the RNAS fin and rudder, cut-down cockpit sides and a large fuel tank in place of the forward crew member, giving an endurance of 8 hours.
(Monochrome Photograph - Showing an Avro 504C fitted with a Type H bomb rack.)
and a 112 lb. (50 kg) bomb.)