The Wehrmacht Heer was from 1935 to 1945 the army section of the German armed forces (Wehrmacht) which also consisted of the navy (Kriegsmarine) and air force (Luftwaffe). During Second World War, a total of about 15 million soldiers served in the German Army, of which about 3 million perished.

The German Army furthered concepts pioneered during the First World War, combining ground (Heer) and Air Force (Luftwaffe) assets into combined arms teams. Coupled with traditional war fighting methods such as encirclements and the "battle of annihilation", the German military managed many lightning quick victories in the first year of the Second World War, prompting foreign journalists to create a new word for what they witnessed: Blitzkrieg.

The Wehrmacht entered the war with a minority of its formations motorized; infantry remained approximately 90% foot-borne throughout the war, and artillery primarily horse-drawn. The motorized formations received much attention in the world press in the opening years of the war, and were cited as the reason for the success of the German invasions of Poland (September 1939), Norway and Denmark (April 1940), Belgium, France and Netherlands (May 1940), Yugoslavia (April 1941) and the early campaigns in the Soviet Union (June 1941).

With the entry of the United States in December 1941, the Wehrmacht found itself engaged in ground campaigns against two major industrial powers. At this critical juncture, Hitler assumed personal control of the Wehrmacht high command, and his personal failings as a military commander arguably contributed to major defeats in the spring of 1943, at Stalingrad and Tunis in North Africa.

Most land battles that the Wehrmacht fought were in the Soviet Union on the Eastern Front. But the Wehrmacht had to fight on simultaneously at all fronts, sometimes surpassing three at once, that stretched its fighting power thin and had an effect, to varying degrees, on Wehrmacht's ability to successfully accomplish the campaigns of conquest that were entrusted to them.

The only strategic air battles that the Luftwaffe proved capable of winning were in 1939 and 1940; the air force was unable to defeat the Royal Air Force in the Battle of Britain and Allied air forces enjoyed aerial superiority on all fronts by the summer of 1944. Although, in respect to the Battle of Britain, had the Luftwaffe continued toward its early goal of bombing RAF airfields and fighting a war of attrition against Britain's air force, it is likely they would have been victorious. However, in response to a string of events beginning with a small scale air raid on Berlin by British bombers, Hitler ordered the German bomber formations to attack English cities. These reprisal attacks allowed the weight of the Luftwaffe to be shifted away from the RAF and onto British civilians, and, thusly, allowed the RAF to rebuild and, within a few short months, turn the tide against Germany in the skies above England.