The NOTS-EV-2 Caleb, also known as NOTS-500, Hi-Hoe and SIP was an expendable launch system, which was later used as a sounding rocket and prototype anti-satellite weapon.

It was developed by the United States Navy's Naval Ordnance Test Station (NOTS)[1] as a follow-up to the NOTS-EV-1 Pilot, which had been abandoned following ten launches officially classified as failed missions.

[1] Following cancellation, two leftover Calebs were used in the Satellite Interceptor Program (SIP), while three more were used as sounding rockets, under the designation Hi-Hoe.

[1]Caleb was an air-launched rocket, with its two launches being conducted from F4D Skyray #747, the same aircraft used in the Pilot trials.

[6] On the first two launches the second stage failed to ignite,[4] however the third was successful, and reached an apogee of 1,166 kilometres (725 mi).