US Navy submarines are key to countering China's naval expansion in the Indo-Pacific.China's military expansion includes a large navy, posing a threat to US naval dominance.US submarines, despite challenges, maintain an edge with advanced capabilities and strategic roles.The threat of a conflict with China has risen tremendously over the years. Beijing is undergoing some of the largest military expansion and modernization efforts since World War II, building a formidable arsenal of missiles able to threaten surface ships and massive naval force, but the US Navy still has the means to sink Beijing's dreams of supremacy in the Indo-Pacific.The US is looking to solutions like anti-ship missiles, but a key answer to China's expanding surface and logistics fleet that could number over 700 ships in a conflict is submarines. A Chinese Type 055 destroyer Photo by Artyom Ivanov\TASS via Getty Images Hunt and SinkThe US Navy would play a leading role in a potential conflict with China in the Indo-Pacific. This region's vast maritime domain is ideal for naval and air operations.China understands that, and Beijing has been investing heavily in its navy, the largest in the world according to the Pentagon. China has built three aircraft carriers with plans for more, possibly nuclear-capable flattops, new amphibious assault ships, and increasingly capable destroyers.Where there are surface warships, there is an opportunity for submarines, and undersea capabilities are an area where the US maintains a clear edge over China, even as it strengthens its force and invests in anti-submarine warfare solutions.An important role for the US submarine force in a conflict would be to hunt and sink Chinese warships and logistical vessels. Sailing routes around Taiwan and in the South China Sea would potentially be ideal hunting grounds for stealthy submarines like those operated by the US Navy.In a war game conducted last year by the Center for Strategic and International Studies simulating an intense fight over Taiwan, the think tank found that "submarines were able to enter the Chinese defensive zone and wreak havoc with the Chinese fleet," but it also found the number of subs available was insufficient, indicating a need to prioritize these capabilities. A Chinese dual-carrier exercise in the South China Sea. People's Liberation Army Attack submarines can be deadly for enemy shipping and change the course of a war. The Falklands War between Argentina and the United Kingdom in 1982 is a perfect recent example of the potential of submarines in a state-on-state conflict.During the war, the Argentine Navy transported men and weapon systems to the islands, creating a lifeline with mainland Argentina about 400 miles away. The Royal Navy went to war 8,000 miles away with six submarines leading the way, and they enforced an exclusion zone around the islands.When the need arose, HMS Conqueror, a nuclear-powered attack submarine, sunk the ARA General Belgrano battlecruiser, one of the largest warships in the Argentine fleet. The shock of the sinking and the potential for further attacks forced the Argentine Navy to withdraw from the area, thus allowing the British ground forces to land unopposed. The attack submarine USS Virginia departing Naval Submarine Base New London en route to Portsmouth Naval Shipyard in Kittery, Maine. US Navy photo/Petty Officer 1st Class Steven Myers Similarly, US submarines could help disrupt or destroy a Chinese amphibious force heading to Taiwan and limit the movements of the Chinese navy across the theater of operations.Submarines aren't unstoppable, though. Advances in anti-submarine warfare have made submarines increasingly vulnerable. For China's navy, ASW has been a growing priority to counter the American sub threat. Additionally, uncrewed undersea vehicles can also pose a threat and help detect prowling subs, as can underwater sensor systems like the US operates and China has looked to as added security.They can't stay under indefinitely without support. Munitions resupply US subs are powered by nuclear force, meaning they don't have to refuel is another challenge, especially in a high-intensity battlefield.And the US faces challenges maintaining its undersea advantage. A key priority in the Navy's fiscal year 2025 budget proposal was investment in the submarine industrial base.Submarine FleetThe US Navy has the largest and most advanced submarine force in the world, with 71 vessels and a lot of variety. And given the challenges from China, much of that capability is in the Pacific.The Navy's submarine fleet is comprised of attack, guided-missile, and ballistic-missile subs. The Los Angeles-class attack submarine USS Helena transiting the Atlantic Ocean. US Navy photo by Mass Communication Specialist 1st Class Rafael Martie/Released Attack subs are the staple of any submarine fleet. Their job is to find and sink enemy ships. The three classes of attack subs in the US fleet (Virginia, Los Angeles, and Seawolf) can do this by sailing stealthily underwater and firing torpedoes and cruise missiles. The Navy has 53 attack subs.Guided-missile submarines support ground and naval forces by firing long-range munitions, but they can also sink enemy shipping via torpedoes. Each of the four Ohio-class guided-missile subs on the active fleet can pack over 150 Tomahawk cruise missiles.Finally, ballistic-missile submarines make up America's maritime arm of the nuclear triad. The 14 Ohio-class ballistic missile submarines carry 20 Trident II ballistic missiles with nuclear warheads each. Although the subs also pack torpedoes like their attack and guided-missile siblings, the main mission of ballistic-missile subs is to rain down destruction in the event of a nuclear conflict.