Zellmer, D. (1999). The spectator: A World War II bomber pilot's journal of the artist as warrior. Praeger.
Cita Chicago (17th ed.)Zellmer, David. The Spectator: A World War II Bomber Pilot's Journal of the Artist as Warrior. Westport, Conn.: Praeger, 1999.
Cita MLA (9th ed.)Zellmer, David. The Spectator: A World War II Bomber Pilot's Journal of the Artist as Warrior. Praeger, 1999.
Atenció: Aquestes cites poden no estar 100% correctes.