"...allowing for multiple simultaneous and devastating deep strikes using Drop Pods. The Codex Astartes calls this manoeuver 'Steel Rain'..."
The term "Steel Rain" refers to one of the many tactics penned by the Ultramarines' Primarch Roboute Guilliman in his Codex Astartes in answer to a specific tactical need. This manoeuvre capitalises on the speedy (re-)deployment of forces through the use of Drop Pods to prevent being bogged down or being forced to commit valuable Space Marine Battle-Brothers to man a static defense line needlessly.
After the dark days of the Horus Heresy, Roboute Guilliman, the Primarch of the Ultramarines Legion, required the surviving Loyalist Space Marine Legions to be divided into Chapters one thousand Space Marines strong. This downsizing brought forth a whole host of tactical problems, for the limited number of Space Marines could no longer grind down an opponent through mass and attrition. Guilliman's reform prompted the Adeptus Astartes' modus operandi to evolve toward quick, overwhelming strikes intended to rapidly crush the head or heart of any opposition immediately, and avoid prolonged operations and grinding attrition wherever possible.
The "Steel Rain" manoeuvre is such a tactic, intended for use on those occasions where a vital objective needs to be defended. Instead of sending part of the Battle-Brothers to defend the objective directly, those Astartes are kept in reserve on board a Strike Cruiser or Battle Barge. The objective itself is monitored, either by automated sensors or by other Imperial forces present, and if it becomes threatened, or if the already deployed Space Marines manage to bring the battle to the enemy, the reserves are quickly deployed where they are necessary via a concerted Drop Pod assault. Once the situation is over, both the Space Marines and their Drop Pods are quickly brought back to the orbiting starship, and readied for the next instance where their assistance is necessary. The focus on using multiple Drop Pods at once has given the tactic the moniker "Steel Rain" or "Rain of Steel," with each Drop Pod serving as one drop of this metaphorical rain.
- Captain Indrick Boreale of the Blood Ravens - The "Steel Rain" was Captain Boreale's favoured tactic, allowing him to quickly deploy his Astartes wherever their presence was required. Unfortunately for him and the Blood Ravens, the tactic did not prove efficient enough to deliver victory in the Kaurava System, and Captain Boreale paid for his over-reliance on quick redeployments with his life.
- Dawn of War - Soulstorm (PC Game)