He flew his first combat missions in the Battle of France, bombing airfields and shipping off Dunkirk for which he was awarded the Iron Cross 2nd Class on 17 July 1940.

Barth was promoted to Oberleutnant and following Operation Barbarossa, the German invasion of the Soviet Union on 22 June 1941, flew in the southern sector of the Eastern Front.

He bombed airfields, railway stations as well as tank and troop concentrations in the Proskurov, Lvov, Rostov and Taganrog areas.

Barth stayed in this position until 31 March 1945 before being appointed Geschwaderkommodore (Wing Commander) of KG 51 on 19 April 1945.

The event came at a historically difficult time during the Cold War, one month after the construction of the Berlin Wall.

[3] Barth took his case to the Wehrdienstsenat des Bundesdisziplinarhofs, the highest court of German troops, to have him cleared of the charges brought against him.