Book excerpt: The bombing of Guernica has become a symbol of Nazi involvement in the Spanish Civil War, but the extent of the German commitment is often underestimated. The Luftwaffe sent 20,000 officers and men to Spain from 1936 to 1939, and the Condor Legion carried out many missions in support of the Spanish Nationalist forces and played a lead role in many key campaigns of the war. Aircraft that would play a significant role in the combat operations of World War II (the Heinkel 11 bomber, the Me 109 fighter, and others) saw their first action in Spain, fighting against the modern Soviet fighters and bombers that equipped the Republican Air Force. Condor Legion bombers attacked Republican logistics and transport behind the lines as well as bombing strategic targets, German bombers and fighters provided highly effective close air support for the front-line troops, and German fighters and anti-aircraft units ensured Nationalist control of the air. The experience garnered in Spain was very important to the development of the Luftwaffe. The war allowed them to hone and develop their tactics, train their officers, and to become the most practised air force in the world at conducting close support of ground troops. In effect, the Spanish Civil War proved to be the training ground for the Blitzkrieg which would be unleashed across Europe in the years that followed. In this rigorous new analysis, Legion Condor expert James Corum explores both the history and impact of the Luftwaffe's engagement during the Spanish Civil War and the role that engagement played in the development of the Luftwaffe strategy which would be used to such devastating effect in the years that followed.