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. These proved to be most useful during Operation Overlord, in the hedgerowed bocage country south of the invasion beaches, for spotting hidden German tanks waiting in ambush for American and British tanks of the invasion forces. Since the L-4 Grasshoppers were mechanically identical to the J-3 civilian version, the military versions were distinguished by the presence of rearwards-entended Plexiglas windows going over the top of the wing and behind the rear-seat passenger, somewhat aft of the wing's trailing edge. Nearly 5,700 L-4s were produced for the U.S. Army and 250 for the U.S. Navy as "elementary trainers".