 Matthews and Foreman, authors of "Luftwaffe Aces — Biographies and Victory Claims", researched the German Federal Archives and state that Gratz was credited with 138 aerial victories.This figure includes 132 aerial victories on the Eastern Front and six over the Western Allies, including one four-engined bomber.Victory claims were logged to a map-reference (PQ = "Planquadrat"), for example "PQ 44442".