Plane Spotter cards were commonly used by U.S. forces to train personnel to recognize aircraft silhouettes.  The card sets included not only enemy aircraft but Allied planes as well. 

Each card resembled the one shown here but also listed the nation and aircraft designation.  If you think you recognize this familiar shape, click on the image to see whether you guessed correctly.

See how well you can do in recognizing other silhouettes.  Choose card decks by nationality or look at the bomber, fighter and transport groups which mix nationalities for a harder test.