Context : Waldemar Semelka (8 January 1920 -- 21 August 1942) was a German Luftwaffe ace and recipient of the Knight's Cross of the Iron Cross during World War II. The Knight's Cross of the Iron Cross was awarded to recognise extreme battlefield bravery or successful military leadership. 
Subject : Waldemar Semelka 
Relation : conflict
What was the war that Waldemar Semelka fought in?