The U.S. has likely been underestimating the number of attack submarines it would need in the Pacific, given the heightened potential for conflict in the region, warned James R. Holmes, professor of strategy at the Naval War College.“You need to divide the number [of total ships] by two, three, or even more to estimate realistically how many ships are available for duty on any given day. The rest are in overhaul, undergoing training, or relaxing after deployment,” Holmes said. “So, divide the number of SSNs in the Pacific by three, then look at the map. That’s very few boats to manage events in the world’s largest body of water.”Nearly half of the $106.4 billion of planned Navy shipbuilding between fiscal 2019 and 2023 will go for nuclear ballistic and attack submarines, according to the Navy’s long-range construction plan. The spending blueprint calls for $32.9 billion for construction of ten attack submarines and $16.7 billion for a new nuclear ballistic submarine.The attack submarines are armed with various cruise missiles designed to hit closer-range land and sea targets. They are specifically designed to attack and sink other submarines, surface combatants and merchant vessels.The nuclear ballistic submarines are equipped with nuclear weapons capable of delivering a retaliatory or preemptive strike almost anywhere in the world. Combined, these two types of submarines make up the preponderance of what will likely be the future of undersea warfare.