Bloem was born in 1898 in Barmen, in present-day North Rhine-Westphalia, Germany as the son of the writer Walter Bloem, noted as an author of patriotic novels, and his first wife Margarete Kalähne. His father e.g. wrote the memoir "The Advance from Mons 1914"—the translation included a foreword by James Edward Edmonds who called it "one of the most graphic and dramatic accounts of the war yet written."