While the G.3 and G.4 had been credited largely to Gaston Caudron, the R.4 was mostly the work of Rene Caudron. Appearing in prototype form in June 1915, the R.4 had a full-length fuselage and single fin and rudder. The unequal-span wings had three bays on each side, with ailerons on the upper wing only. As well as the twin-wheel main landing gear units and tailskid, there was a single nose-wheel intended to protect the propellers. Power was from twin 97kW Renault i2Db engines. The three-man crew included nose and midships gunners each provided with twin Lewis machine-guns.
Intended originally as a bomber, it served mainly as an A.3 category three-seat reconnaissance aircraft, frequently engaged in photographic work. Its climb rate was not impressive, and a few aircraft were built with more-powerful 112kW Hispano-Suiza 8Aa engines in an attempt at improvement.
The production aircraft began to reveal a structural weakness. Among the crashes that happened, on 12 December 1915, a series aircraft under test was destroyed and Gaston Caudron, who was piloting the aircraft, was killed.
In early use Escadrille C.46 had claimed 34 German aircraft brought down with its R.4s in an eight-week period, but it was soon clear that in addition to structural redesign, improved ceiling and greater manoeuvrability were highly desirable. The new Caudron chief designer, Paul Deville, designed a new improved development which was to emerge as the R.11.
Production of the R.4 was terminated after 249 had been built. In the reconnaissance escadrilles it was replaced by the more-powerful Letord 1 during 1917.
Engine: 2 x 97kW Renault 12Db inline piston engines
Take-off weight: 2330 kg / 5137 lb
Empty weight: 1710 kg / 3770 lb
Wingspan: 21.1 m / 69 ft 3 in
Length: 11.8 m / 38 ft 9 in
Wing area: 70 sq.m / 753.47 sq ft
Max. Speed: 136 km/h / 85 mph
Ceiling: 4600 m / 15100 ft
Armament: 4 x 7.7mm machine guns, 100kg of bombs