Article: On 6 April 1941, German forces, with Hungarian and Italian assistance, launched an invasion of Yugoslavia. On 10 April 1941, Slavko Kvaternik proclaimed the Independent State of Croatia, and Tito responded by forming a Military Committee within the Central Committee of the Yugoslav Communist Party. Attacked from all sides, the armed forces of the Kingdom of Yugoslavia quickly crumbled. On 17 April 1941, after King Peter II and other members of the government fled the country, the remaining representatives of the government and military met with the German officials in Belgrade. They quickly agreed to end military resistance. On 1 May 1941, Tito issued a pamphlet calling on the people to unite in a battle against the occupation. On 27 June 1941, the Central Committee of the Communist Party of Yugoslavia appointed Tito Commander in Chief of all project national liberation military forces. On 1 July 1941, the Comintern sent precise instructions calling for immediate action.

Question: When did German forces launch an invasion of Yugoslavia?
6 April 1941