This is a reel with a coil of 1/8 inch (0.32 cm) steel cable, 150 ft. (45.7 m) long, for use with the Wadsworth Mount grapnel line throwing rocket, which was tested 1944-1945 using standard U.S. Navy and other ordnance rockets.
The rocket system was developed by the American inventor Wadsworth Mount (1907-1985) for the purpose of throwing life lines for rescue work at sea, or from ship to shore as life saving rockets and used standard U.S. Navy 1.25-in (3.175 cm) and 3.25-in (8.26 cm) rockets. The grapnel rockets were also to be used to climb cliffs and for breaching beach defenses. However, the system was not adopted by the military. Mount donated the reel, along with the full kit, to the Smithsonian in 1976.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.