Modern missile systems routinely pass component-level testing only to fail upon full integration, where electromagnetic interference, power dynamics, timing conflicts, and cross-subsystem dependencies expose critical vulnerabilities. Discovering these failures during live-fire tests costs millions of dollars and derails program schedules by months. Missile TestBench Level 3 addresses this challenge by delivering full-system Hardware-in-the-Loop (HIL) validation with 36-core real-time compute, deterministic microsecond timing, high-density heterogeneous I/O, and comprehensive mission simulation. Integration defects surface immediately on the test bench rather than on the range, significantly cutting integration cycles and eliminating timing-induced test failures before they threaten the program or the mission.