Camel.
 
Arguably the best allied fighter of WWI was the Sopwith F1 Camel. With its distinctive rotary engine and twin synchronised machine guns, it accounted for many German fighters. Photo details: Canon 40D, ISO 400, 1/500th second exposure with a Canon EF 70-200mm IS USM lens @ f-8.

 Image taken January 18th 2009