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 L-4 Grasshopper was mechanically identical to the J-3 civilian Cub, but was distinguishable by the use of a Plexiglas greenhouse skylight and rear windows for improved visibility, much like the Taylorcraft L-2 and Aeronca L-3 also in use with the US armed forces. Carrying a single pilot and no passenger, the L-4 had a top speed of 85 mph, a cruise speed of 75 mph, a service ceiling of 12,000 ft (3,658 m), a stall speed of 38 mph, an endurance of three hours,
and a range of 225 mi. 5,413 L-4s were produced for U.S. forces, including 250 built for the U.S. Navy under contract as the NE-1 and NE-2.