Early reconnaissance types had proved the value of aircraft at the battle front and by 1916 all major air forces were carrying out expansion programmes. The C.IV was built by AEG as a follow-on to the unsuccessful C.III, although it reverted to the general configuration of the Ñ.II. Produced by AEG and Fokker, many C.IV were operated successfully in reconnaissance and observation roles by the German Air Force right up to the Armistice. Others went to the air forces of Bulgaria (which declared war on Romania in September 1916) and Turkey (engaged in war from 1914, but most Turkish Flying Corps aircraft flown by German pilots). Despite proving to be underpowered, C.IV were also used as escorts, while a night bomber variant (C.IVN) was produced in prototype form in 1917. It had a wing span of 15.3m and a 112kW Bz.III engine. Another variant was built as the C.IVa, powered by a 134kW Argus engine.