The Caudron R.11 (aka R XI) was the last bomber the French built during the Great War.
Evolved by Paul Deville from the R.IV reconnaissance bomber designed by Rene Caudron, the R.11 three-seat biplane was originally intended as a Corps d'Armee aircraft, but was destined to find its forte as a three-seat escort fighter. Its design was similar to the Caudron R.4, but with a more pointed nose, two bracing bays outboard the engines rather than three, no nose-wheel, and a much larger tail.
The engines were housed in streamlined nacelles just above the lower wing. The French army ordered 1000 R.11s. Production began in 1917. Powered by two 215hp Hispano-Suiza 8Bda eight-cylinder water-cooled engines, the R.11 appeared in March 1917, and entered service in February 1918, when the first Escadrille (squadron) R.26 was equipped. The last escadrille to form before the Armistice (and production ended abruptly) was R.246, at which point 370 planes had been completed.
Armament comprised five 7.7mm Lewis guns on flexible mounts - two in the nose cockpit, two in the dorsal cockpit and one firing downwards and rearwards beneath the front gunner's cockpit - and while initial models retained the HS 8Bda engines, later versions were fitted with the 235hp HS 8Beb.
The R.11 enjoyed considerable success as an escort for the Breguet 14 during the closing months of WWI and during the summer of 1918. It also served in the fighter-reconnaissance role. At the time of the Armistice, the R.11 equipped six 15-aircraft escadrilles of France's Aviation Militaire. A more powerful version, the R.11I with 300hp HS 8Fb engines, was tested during the summer of 1918, but apparently failed to display significantly better results than those obtained with the R.11. Prototype trials with the R.11I were completed in the autumn of 1919, but no further development was undertaken.
The successful use of these Caudrons as escort fighters established a French trend towards the development of multi-seat combat aircraft, a category that became known as the "multiplace de combat". The French continued to experiment with this category of aircraft throughout the 20s and 30s, and even influenced air forces in other countries to do the same.