From a naval perspective, the Chinese People’s Liberation Army Navy (PLAN) is pursuing a mix of high-end and low-end ships and submarines. This strategy would allow the PLAN to spread out across the vast Pacific Ocean in sufficient numbers to locate and interdict U.S. ships. At the high end, China is investing in aircraft carriers, nuclear-powered fast-attack submarines and large surface combatants equipped with advanced radars, surface-to-air missiles (SAMs) and surface-to-surface missiles. While China’s high-end ships are designed to go toe to toe with their American counterparts in battle, Beijing is unlikely to close the United States’ technological head start. Therefore, China is aiming to close the capability gap by fielding mass quantities of low-end ships.

While the United States will not start buying frigates until the 2020s, China is building a new frigate every six weeks. Vast numbers of these low-end ships will increasingly patrol China’s expanding front lines in the western Pacific and Indian Ocean regions. Backed by a growing arsenal of longer-range and more sophisticated air and missile weapons, the Chinese navy will have a highly capable and numerically larger maritime force by the middle of the next decade. If this situation comes to fruition, it could make the projection of U.S. naval power cost prohibitive in the western Pacific, undermining the credibility of our alliance commitments. Indeed, China currently calculates that western Pacific nations—South Korea, Japan, Taiwan, the Philippines and perhaps even Australia—may ultimately align with the Middle Kingdom.

As China develops a comprehensive suite of A2/AD capabilities, Vladimir Putin’s Russia is making a different strategic bet. Faced with a shrinking population and weak economy, Putin has chosen to invest in small numbers of advanced A2/AD systems that pack a tremendous punch. In the past decade, Russia has fielded a new SAM system—the S-400 Triumf—that is highly maneuverable and lethal, with a 250-mile range. What’s more, Putin’s military has employed 1,500-mile Kalibr cruise missiles, recently launching them from a submarine in the Black Sea against targets in Syria. Russian Iskander surface-to-surface missiles are designed to block American entry into the Baltic Sea, the Black Sea or even the eastern Mediterranean.

From a naval perspective, Russia has always prioritized its submarine fleet. The newest Russian submarine—the nuclear-powered Yasen-class guided-missile submarine—should give U.S. naval planners pause. Extremely quiet, difficult to detect, and carrying a heavy load of torpedoes and antiship cruise missiles, one or two Yasens undetected in the Atlantic could effectively halt American efforts to provide relief to NATO allies. If Russia shared the noise-quieting techniques used on the Yasens with China, it could dramatically erode the United States’ technological advantage in the undersea realm.

Iran presents a different set of challenges. As a regional power, its naval operations are largely constrained to the Arabian Gulf and the Gulf of Oman (although Iran has attempted to deploy some ships beyond its near seas). However, Iran directly overlooks the Strait of Hormuz, through which some 20 percent of the world’s petroleum passes. Hormuz is only twenty miles across at its narrowest point, and its shipping channel, where deep-draft tankers pass, is only a few miles wide. Assuring access to this maritime “choke point” is clearly a vital interest for the United States and many of its allies and partners.

Iran is developing low-end A2/AD capabilities to threaten access to Hormuz in a crisis. While the Iranian Navy is comprised of small frigates and diesel-electric submarines (purchased from Russia), Iran’s other maritime force—the Islamic Revolutionary Guard Corps (IRGC) Navy—presents the real A2/AD problem for U.S. naval forces.

The IRGC Navy specializes in small torpedo, missile and patrol boats. Operating in the relatively calm waters of the Arabian Gulf, IRGC fast boats could operate in large “swarm” formations, running in swiftly and cutting across the bows of American and allied warships. Swarming boat attacks could deter or overwhelm U.S. naval forces by sheer numbers, sacrificing many boats to get one technologically advanced ship. The swarm-boat scenario is a serious operational challenge: In 2000, the Arleigh Burke–class destroyer USS Cole was nearly sunk by terrorists operating a simple motorboat in Yemen.

Just as our maritime interests have evolved, so have the threats to U.S. power projection from the sea. Our adversaries and potential opponents are racing forward to develop A2/AD capabilities to create maritime “keep-out zones.”

EITHER BY commission or omission, the United States is simply not upholding its maritime interests in the face of these emerging threats. The evidence is voluminous, such as our actions regarding China during the Obama administration, when the Navy reached its modern nadir of 271 ships. By not maintaining a credible and persistent naval presence in the South China Sea, the United States invited China to create a “Great Wall of Sand”—a series of artificial islands that increasingly resemble military garrisons. The United States did nothing when China established a military cordon around the Philippine claim at Scarborough Shoal in 2012. The Philippines is a claimant to Scarborough, and America’s oldest Asian treaty ally. This inaction raised doubts about the United States’ reliability as a security partner.

In the absence of strong American sea power, Russia has also begun to assert territorial claims and advance its sovereignty in the Arctic, going so far as to plant a Russian flag on the bottom of the Arctic Ocean at the North Pole. Likewise, Russia has begun aggressive operations in the Baltic and Black Seas, seeking to intimidate U.S. Navy ships as well as those of allied and partner navies. The United States has offered no serious response to these provocations.

Lastly, despite a long-standing military requirement to maintain one carrier strike group continuously in the Arabian Gulf region, the ever-shrinking U.S. Navy has been forced to leave the region without a serious naval presence multiple times in recent years. Training and maintenance backlogs within the hollowed-out Navy have reduced the available carrier inventory to provide coverage to the Arabian Gulf. During these periods, Iran has ramped up its intimidation operations and actively sought to undermine the credibility of the United States and its partners in the region. In 2016, Iran’s Houthi allies in Yemen had the audacity to conduct an unsuccessful missile attack against a U.S. warship, USS Mason.

AMERICA’S MARITIME interests are growing. This, in turn, complicates efforts to protect U.S. interests and confront new threats. The United States currently has a navy too small for the requirements of a great naval power. Following the Fitzgerald and McCain collisions, the secretary of the navy, Richard V. Spencer, commissioned a Strategic Readiness Review to identify the long-term causal factors that contributed to the rash of accidents in the western Pacific. The review concluded that “the growing mismatch between the supply and demand of ships taxed fleet personnel and consumed material readiness at unsustainable rates.” Too few ships fulfilling too many missions degraded the combat readiness of ships and sailors alike.

After the Cold War, the Navy battle fleet stood at 529 ships. Yet, on the eve of 9/11, the Navy had shrunk to 316 ships. Today, the Navy has 282 ships. Overall, the fleet size has been cut by about half over the past quarter century. The decline in supply has not been matched by less demand for naval power. The number of ships needed for operations has remained steady despite a smaller inventory of available ships, and the Navy has struggled to maintain eighty-five to one hundred ships underway at all times. Until the mid-1990s, when the fleet hovered around four hundred ships, it was possible to maintain this deployment cycle. However, the steps necessary to meet requirements for underway ships became extremely dangerous in the late 1990s. Fleet size declined to the 350-ship level before bottoming out at 271 ships in 2015. As shown by the Fitzgerald and McCain, it has become life-threatening to keep the necessary ships at sea without compromising maintenance, training and readiness certifications. The secretary’s review described the situation as the “normalization of deviation,” or an institutionalized pattern of bending the rules to get the mission done.

The United States has critical national interests in eighteen maritime zones identified by warfighting commanders. These maritime regions range in size from the small Gulf of Guinea to the vast northern Pacific and from the northern Arctic Sea to the Indian Ocean.

Each zone requires a naval presence to uphold American interests. Some of these zones, like the Baltic Sea, require only a single American ship to protect and promote our interests, while others, like the Arabian Gulf, have a standing requirement for an aircraft carrier strike group comprised of six to eight ships, as well as permanently stationed coastal patrol boats. Because of ship maintenance, crew training and transit times, providing a naval presence requires three to four ships to keep one forward deployed. All told, the Navy needs a minimum of 355 ships to keep a naval presence on a credible and persistent basis, if the United States wants to maintain freedom of navigation, protect resources and undersea critical infrastructure, and uphold its alliance agreements. The Navy certified the 355-ship requirement in its 2016 Force Structure Assessment (FSA). According to the FSA, the true number of ships required by military commanders exceeds 650 ships. Importantly, achieving the 355-ship fleet is not just a Navy requirement; it is a matter of complying with U.S. law. Signed by President Trump in December 2017, the defense authorization bill for fiscal year 2018 includes the SHIPS Act, legislation establishing the 355-ship requirement as the national policy of the United States.