Code Name: Viper, originally released as Ningen Heiki: Dead Fox (人間兵器デッドフォックス, The Human Weapon: Dead Fox) in Japan, is a side-scrolling action game released by Capcom in 1990 for the Nintendo Entertainment System. The player takes control of a special forces operative who must combat a drug syndicate in South America.

The gameplay system is similar to Namco's 1986 arcade game Rolling Thunder. Like in Rolling Thunder, the player can jump or drop down between floors by holding the directional pad up or down and pressing the jump button, as well as enter doors to obtain power-ups or avoid enemies. The player can be armed with one of two weapons (a standard issue pistol or a semi-automatic machine gun for continuous firepower). Items includes additional ammunition for either weapon, extra health, a time extension, and extra lives. Unlike Rolling Thunder, the player can shoot while jumping and can also change directions during midair.

Another difference between Rolling Thunder and Code Name: Viper is the added emphasis on rescuing hostages. Throughout the first seven stages, the player can find captured civilians behind certain doors, who will offer the player their gratitude. However, if the player takes too long to rescue certain hostages, the player will only find their skeletal remains. To complete each of the first seven stages, the player must rescue a captured commando who will provide the grenades necessary to blow up the obstruction blocking the exit at the end of each stage.

The strength and attack patterns of the standard enemy soldiers that the player will face is determined by the colors of their outfit. In addition to the standard enemy soldiers will face other adversaries such as Snipers, Frogmen, and Maniacs. There are a total of eight stages, with three difficulty settings.