The H-1 upgrade program is the United States Marine Corps's program to develop the AH-1Z Viper and UH-1Y Venom military helicopters to replace its aging fleets of AH-1W SuperCobras and UH-1N Twin Hueys. The contract was awarded in 1996 to Bell Helicopter, the original manufacturer of both aircraft, to design the new airframes as modernized attack and utility helicopters with considerable design commonality, to reduce operating costs.

The Bell AH-1Z Viper is a twin-engine attack helicopter, based on the AH-1W SuperCobra, designed and produced by the American aerospace manufacturer Bell Helicopter. It is one of the latest members of the prolific Bell Huey family. It is often called "Zulu Cobra", based on the military phonetic alphabet pronunciation of its variant letter.