By Duane J. Truitt The U.S. Navy is faced with several big challenges in maintaining undersea warfare dominance – the domain of the fast attack nuclear submarine or “SSN.” These challenges include the reemergence of a near peer naval threat that is a direct challenge to the entire U.S. Navy, including our SSN force. The current and growing undersea threat includes both advanced technology attack submarines (including nuclear, diesel-electric, and air independent propulsion variants) with advanced torpedoes and cruise missiles, and much increased numbers of adversary submarines, particularly in the Indo-Pacific theater. Another challenge comes from the rapidly escalating procurement and sustainment costs of ever-larger and more complex U.S. SSNs since the end of the Cold War.