Oberst Johannes Bässler served as Chief of Staff of XI Army Corps at the start of World War II, and participated in the Invasion of Poland in this capacity, during which he was awarded the Iron Cross, First Class and Second Class. He remained in the General Staff of XI Corps until 21 February 1942, and participated in the Battle of France, the Invasion of Yugoslavia, and Operation Barbarossa, the latter as part of Army Group South. He was promoted to Generalmajor on 1 February 1942.
Bässler took command of 9th Panzer Division on 15 April 1942 in the area east of Kursk, around the town of Shchigry on the Eastern Front. In July 1942 the unit was involved in heavy fighting to secure the German northern flank around Zemlyansk, northwest of Voronezh, when Bässler was seriously wounded and had to leave his command on 27 July 1942. After recuperating, on 16 November 1942, he took command of 14th Panzer Division until 26 November 1942, when the division was put into reserve in the Don River curve behind the Romanian front in the area.
He was awarded the German Cross in Gold on 9 January 1943 for his actions commanding the 9th Panzer Division. He returned to active duty in June 1943, and was assigned to command 242th Infantry Division in the Toulon, France on 7 July 1943. In conducting the defense of the city and port against advancing American and French forces, Generalleutnant Bässler (promoted on 1 February 1944) was critically wounded on 26 August 1944, and died of his wounds in a reserve hospital in Vienna on 9 November 1944.
- Iron Cross (1914)
- Honour Cross of the World War 1914/1918
- Iron Cross (1939)
- German Cross in Gold (1 August 1943)
- Battle of France
- Invasion of Yugoslavia
- Operation Barbarossa
- Battle of the Caucasus
- Battle of Stalingrad
- Battle of Toulon (1944)