Operation Barbarossa
Operation Barbarossa (named for Frederick Barbarossa
Frederick I, Holy Roman Emperor
Frederick I Barbarossa was a German Holy Roman Emperor. He was elected King of Germany at Frankfurt on 4 March 1152 and crowned in Aachen on 9 March, crowned King of Italy in Pavia in 1155, and finally crowned Roman Emperor by Pope Adrian IV, on 18 June 1155, and two years later in 1157 the term...

, the medieval German ruler who, as myth had it, would rescue Germany in her time of need) was the code name
Code name
A code name or cryptonym is a word or name used clandestinely to refer to another name or word. Code names are often used for military purposes, or in espionage...

 for Germany
Nazi Germany
Nazi Germany , also known as the Third Reich , but officially called German Reich from 1933 to 1943 and Greater German Reich from 26 June 1943 onward, is the name commonly used to refer to the state of Germany from 1933 to 1945, when it was a totalitarian dictatorship ruled by...

's invasion of the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

 during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 that began on 22 June 1941. Over 4.5 million troops of the Axis powers
Axis Powers
The Axis powers , also known as the Axis alliance, Axis nations, Axis countries, or just the Axis, was an alignment of great powers during the mid-20th century that fought World War II against the Allies. It began in 1936 with treaties of friendship between Germany and Italy and between Germany and...

 invaded the USSR along a 2900 km (1,802 mi) front., the largest invasion in the history of warfare. In addition to the large number of troops, Barbarossa involved 600,000 motor vehicles and 750,000 horses.