HAVE QUICK is a military system to protect UHF radio traffic.

Since the end of World War II U.S. and allied military aircraft have used AM radios in the 225-400 MHz UHF band for short range air-to-air and ground-to-air communications. Military planners made no provision for securing these communications on tactical aircraft and helicopters or protecting them from jamming into the post-Vietnam War era. Progress in electronics in the 1970s reached a point where anyone with an inexpensive police scanner could intercept tactical military communications. Jamming was not much harder.

The HAVE QUICK program was a response to this problem. It recognized that newer aircraft radios already included all-channel frequency synthesizers along with keyboards and displays for data entry. All that was needed was an accurate clock and a microprocessor to add frequency hopping to these radios.

Aircraft and ground radios that employ HAVE QUICK must be initialized with accurate time of day (usually from a GPS receiver), a word of the day which serves as a key and a net number (allowing multiple network to use the same word of the day). The word of the day, time of day and net number are input to a cryptographic pseudorandom number generator that controls the frequency changes.

HAVE QUICK is not an encryption system, though many HAVE QUICK radios can be used with encryption, e.g. the VINSON system. HAVE QUICK is not compatible with SINCGARS, the VHF - FM radios used by ground forces, which operate in a different radio band and use a different frequency hopping method; however some newer radios support both.

HAVE QUICK was well accepted and most U.S. military aircraft now use it (2004). Improvements include HAVE QUICK II and the Second generation Anti-jam Tactical UHF Radio for NATO (SATURN). The latter features faster frequency hopping. HAVE QUICK is expected to be replaced by the Joint Tactical Radio System sometime after 2008.