The Real-Time Analysis for Particle Transport and In-Situ Detection (RAPID) code system utilizes the multi-stage response-function transport approach with the fission matrix method for neutronics simulation of nuclear systems. RAPID performs real-time calculations by utilizing pre-calculated databases for different enrichments, burnups, and cooling times. This paper discusses the validation of RAPID using the U.S. Naval Academy's subcritical reactor facility. Computational validation is performed by detailed comparison with a Monte Carlo N-Particle reference calculation, and experimental validation is performed using both in-core and ex-core neutron measurements with different helium-3 (3He) proportional counters. These measurements and associated calculations have demonstrated that RAPID achieves accurate results in real time.