Reinforcement Ready comes from Command and Conquer: Red Alert 2, the real-time strategy game released for PC in 2000, where an Allied announcer alerts the player that new units are ready. The line was part of the game's distinctive command feedback, and as gameplay clips, edits, and soundboards spread online, it became shorthand for backup arriving. It endures because the phrase is short, instantly understandable, and tied to a well-loved strategy classic, making it useful far beyond its original battlefield context.