Steel Rain
Steel Rain is a defensive tactic employed by Space Marines.
Because a Space Marine Chapter often sends only a fraction of its forces to any given conflict, it is difficult for them to defend a position; if they attempt to cover the entire perimeter, they will be spread too thin to hold off a massed assault, but the only way to strengthen their defense at key points is to leave large sectors undefended.
The Codex Astartes contains a solution to this catch-22: keep the majority of the force's Marines in orbit and deploy automated beacons around the perimeter. A beacon that detects enemies passing through can call down multiple, simultaneous, and devastating defensive Deep Strikes on its position to deal with the enemy force, no matter where on the perimeter they attempt to break through. This way, the Marines need not waste time and effort on territory which does not come under attack, while not leaving any openings to the enemy.
We only hear about it in Dawn of War: Soulstorm, as Captain Indrick Boreale describes it to the Blood Ravens under his command. The funny part is that, if it's in the Codex Astartes, they should all know about it already.
The real reason its never use is because Space Marine chapters rarely set up a base as they normally show up hit the biggest targets and leave, and when they do they're working with the local PDF/Imperial Guard so don't need to use marines to defend the area.
The hilarious part is the fact that Tau describe this Space Marines tactics as unorganised waste of men, that cost Boreale victory.
See Also
- Drop Pods, the vehicles frequently used in Steel Rain (one might say that they are the Steel Raindrops).
- Steel Rehn, a parody song written to the tune of Tay Zonday's "Chocolate Rain" song, but with lyrics sung by Captain Boreale.