This map was made by Dario Casali of Valve Software.

These are some comments by Gabe Newell about the map:
The principal is the same as in Crossfire. There is a bunker which can be used to call a nuclear strike against anyone outside of it every four minutes. Once the strike has been called, a one minute warning siren activates, giving everyone the chance to get to the bunker. There are far more tactical points in this map than in Crossfire and it also addresses the bug in the Crossfire where people wouldn't get killed by the strike sometimes.