Say Hello to the JN-4D ‘Jenny,’ the Backbone of U.S. Postwar Aviation It went on to become the first mass-produced American aircraft, and the two-seater was widely used for training by American and Canadian pilots during the First World War. Here's What You Need to Remember: The Jenny was notable for other significant “firsts”—including becoming the first to fly U.S. Air Mail and the first to be used in tests for “plane-to-plane” and “ground-to-plane” communication. After the end of the First World War military aircraft were sold as surplus and the Jenny was popular among the 1920s era “barnstorming” exploits.