Piper developed a military variant ("All we had to do," Bill Jr. is quoted as saying, "was paint the Cub olive drab to produce a military airplane"),variously designated as the O-59 (1941), L-4 (after April 1942), and NE (U.S. Navy). The variety of models, as well as similar, tandem-cockpit accommodation aircraft from Aeronca and Taylorcraft, were collectively nicknamed “Grasshoppers” and used extensively in World War II for reconnaissance, transporting supplies and medical evacuation.L-4s were also sometimes equipped with lashed-on infantry bazookas for ground attack. Mechanically identical to the J-3, the military versions were equipped with large Plexiglas windows extending over the top of the wing and behind the rear-seat passenger, and the side windows were enlarged. Nearly 5,700 L-4s were produced for the U.S. Army and 250 for the U.S. Navy as "elementary trainers".