The motto of Defcon is "everybody dies". Made by independent developer Introversion Software, the game simulates a global thermonuclear crisis. The game board is of the world map of the 1980s, with the visual style drawing inspiration from the movie Wargames.
Introversion intentionally took a sparse style, both visually and aurally, with the game. Instead of opting for a hyperrealistic depiction of the world, all the countries are outlined in glowing neon lines, with explosions being glowing white circles and units represented by icons. The goal is to make it appear like a command center heads up display from the 80s.
The sounds follow this template as well. There are no screaming jets, exploding torpedos, or anything small-scale. The only time you'll hear something is when a major event occurs, i.e. a nuclear missile hitting a city. Even then, it's merely a low rumble. It is striking how it can chill your blood as LONDON HIT - 28 MILLION DEAD appears on your screen with nothing but a whimper from your speakers.
Stylistically Introversion wanted to put players in a heavily fortified underground bunker (this is all implied, as all you see is the war room display), giving off a detached and heartless feel to the spectacle of nuclear war.
The gameplay consists of 5 phases, where the countries will step up from Defcon 5 (minimal alert) to 4, 3, 2, and finally Defcon 1. With each heightening of security, players have increasingly devastating actions and paranoia will increase.
In Defcon 5, players place their missile silos. These can be used for both offense and defense - you'll need them to shoot missiles at enemies, but they're also the only things that can shoot down incoming missiles as well. As the goal is to nuke your opponents' cities, silos tend to be located near cities with large populations to protect them. Beyond silos, players will also place their various units within their countries boundaries. Units include submarines, fleets, jets, bombers (both are launched from airports).
In Defcon 4, players begin to move their units around. Because missiles can only target things that have been seen, the different units must be moved around to scout out enemy positions. A very intricate dance ensues as players try to manuver units without being spotted and form alliances.
In Defcon 3, units can start attacking one another. Generally this happens very quickly as units are bound to run into each other as they continue their scouting. It is at this point that units start taking dominant positions in which to attack further.
Defcon 2 is the last few moments for players to form alliances (while preparing to break them as soon as backs are turned) and additional warfare happens between units.
In Defcon 1, missiles can finally be launched. Firing first is generally disadvantageous, as it gives away the position of your silo, but players can stagger multiple missile launches such that an opponent can not defend against the onslaught.
There tends to be an uneasy peace as nobody is sure who to attack first, but the truce will soon break and the screen fills with the trajectories of nuclear missiles.
There is no real winner.
Players are ranked according to the number of enemy civilian casualties they inflict.
The message behind Defcon is very simple: in thermonuclear war, everybody dies. Everybody loses. We all know that. What Defcon does is let us see for ourselves.