The Luftwaffe recognized the difficulty of hitting moving ships during the Spanish Civil War.[2] Dipl. engineer Max Kramer, who worked at the Deutsche Versuchsanstalt für Luftfahrt (DVL) had been experimenting since 1938 with remote-controlled free-falling 250 kg (550 lb) bombs and in 1939 fitted radio-controlled spoilers.[3] In 1940, Ruhrstahl was invited to join the development, since they already had experience in the development and production of unguided bombs.[4]