In mid-2019 the U.S. Navy established an Aggressor Squadron (AGGRON) to provide submarine and ship crews with better information about their ASW (Anti-Submarine Warfare) capabilities versus potential opponents. This is mainly for submarine crews as AGGRON is part of the UWDC (Undersea Warfighting Development Center). The United States has the largest submarine force in the world with 54 SSN (nuclear attack subs) and 14 SSBNs (ballistic missile carrying subs). The rest of the world has about 450 submarines, most of them non-nuclear and all trained and equipped to try and deal with American subs.
The latest StrategyPage SUBMARINES update.