HAVE QUICK is a frequency-hopping system used to protect military 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. During development and the procurement of UHF radios, military planners did not require features to secure communications for aircraft and helicopters from jamming until the post-Vietnam War era. Progress in electronics in the 1970s reached a point where anyone with an inexpensive radio frequency scanner or receiver set could intercept military communications. Once the target frequencies were identified, radio frequency jamming could easily be employed to degrade or completely disable communications.

The HAVE QUICK program was a response to this problem. Engineers recognized that newer aircraft radios already included all-channel frequency synthesizers along with keyboards and displays for data entry. The only other system requirement to achieve the desired Anti-Jam functionality were an accurate clock (for timed synchronization) and a microprocessor to add frequency hopping to existing radios.

Aircraft and ground radios that employ HAVE QUICK must be initialized with accurate Time Of Day (TOD) (usually from a GPS receiver), a Word Of the Day (WOD) which serves as a key, and a NET number (providing mode selection and multiple networks 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 KY-58 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 adopted and as of 2007 nearly all U.S. military aircraft use it. Improvements include HAVE QUICK II Phase 2, and a "Second generation Anti-Jam Tactical UHF Radio for NATO" called SATURN. The latter features more complex frequency hopping.

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