The Condor Legion (German: Legion Condor) was a unit composed of volunteers from the German Air Force (Luftwaffe) and from the German Army (Wehrmacht Heer) which served with the Nationalists during the Spanish Civil War of July 1936 to March 1939. The Condor Legion developed methods of terror bombing which were used widely in the Second World War shortly afterwards. The bombing of Guernica was the most infamous operation carried out by the Condor Legion. Hugo Sperrle commanded the unit's aircraft formations and Wilhelm Ritter von Thoma commanded the ground element.