The Heinkel He-51 was developed for the Luftwaffe and entered service in 1934. It was used in combat in 1936 in the Spanish Civil War and after some initial success, it began to be out-classed and had to be switched to ground attack duty. A float-plane version was also built.

The He-51 was used by Bulgaria, Germany, and Spain.

The He-51B was armed with 2 x 7.92 mm machine guns.
The He-51C could also carry 6 x 10 Kg bombs.