Defcon 5 is set in a far future where conflict has decreased and outdated defense bases are being replaced with automated software. You play as an engineer sent to update one such base. Just after uploading the automating code, the base is invaded by unknown assailants from the air and ground. You must rely on your wits and the defense software to fend them off.
Defcon 5 features first-person gameplay inside a complex with maze-like living areas connected to manned turrets outside. You shuttle between shooting down waves of fighters in the turrets and scouring the base levels for card keys during downtime. The game takes place on the Playstation console.
The "Virtual Operating System" controls all major base functions, allowing you to repair damage from attacks, monitor intruders, and place robot sentries. As you find more access keys, you can increase the software's efficiency, eventually commanding turrets remotely or setting them to auto-attack with success. This increases your time to search for additional keys.
Your ultimate goal is to find the clearance to self-destruct the base, defend your escape shuttle, and escape alive. The game demands strategy as defending the base becomes more automated and efficient.