THE GLOBAL maritime system has begun to fray and tatter. American leadership wove together the threads of this fabric—international laws, accepted norms, mutual security and free trade—following World War II. Now, after a generation of unchallenged U.S. maritime preeminence, things have changed. American maritime interests have evolved beyond simply protecting freedom of navigation. Resource exploration and securing undersea “critical infrastructure” have made the maritime domain more important than ever. Threats to those interests have also evolved, and are multiplying rapidly in number and sophistication. The United States faces not one, but two emerging naval powers—Russia and China—challenging its maritime dominance.

Unfortunately, the United States has increasingly failed to uphold its maritime interests. The Navy battle fleet is the primary instrument used by the United States to secure and, if necessary, defend them. Yet the fleet’s size and condition reveal serious shortcomings. On the most basic level, the fleet averaged 740 ships in the post–World War II era but currently stands at only 282 ships. Though our sailors and Marines remain second to none, the condition of the fleet has deteriorated as the need for naval power has far outstripped the supply of available ships. The results of this supply-demand mismatch are longer deployments; hundred-hour workweeks; and deferred, delayed and canceled maintenance and training. This long-term downward spiral in combat readiness has contributed to avoidable incidents such as the USS John S. McCain and USS Fitzgerald collisions that recently resulted in the deaths of seventeen sailors in the western Pacific.

American maritime interests, threats to those interests and responses to those threats have changed and created a new context in which the United States must rebuild its naval power. The White House, the Pentagon and Capitol Hill need a renewed appreciation for America’s interests at sea and the seriousness of the emerging threats to them. Simply put, the United States must engage in a long-term, aggressive campaign to build a larger and more capable battle fleet in order to deter rising competitors, head off a potential arms race and prevent a destabilizing of the international environment. It is U.S. law that the Navy achieve its stated minimum force-structure requirement of 355 ships. The United States should meet this benchmark within ten years.

MARITIME INTERESTS are so embedded in our nation’s history that policymakers and the public often take them for granted. Even the vastness of the world’s oceans has seemingly diminished, given the ease of today’s air travel and an internet that can connect far-flung places. Yet it is important to remember the significance of the oceans and inland freshwater Great Lakes for America’s economic prosperity. 39 percent of Americans, nearly 125 million people, live in counties that directly touch oceanic shorelines. Three million jobs are directly tied to the oceans or Great Lakes, and those jobs contribute $352 billion to the nation’s economic output. Nearly 80 percent of U.S. export trade by tonnage moves over water, and 90 percent of general cargo moves via container ships. The national maritime transportation system carried $1.5 trillion in cargo to and from American ports last year. America’s allies and partners also heavily rely on seaborne transportation. About 95 percent of the globe’s total commerce flows over the seas.

Protecting freedom of navigation is thus a paramount U.S. interest. This core interest—manifested in unimpeded transit in international waters and access to foreign ports for commercial trade—has endured since the republic’s founding. In fact, the abridgement of this core interest served as a predicate for both the American independence movement and the subsequent first defense of the new nation during the War of 1812. The United States was, then and today, a commercial trading nation.

Although freedom of navigation remains central, our maritime interests have evolved beyond simply securing the seas for commercial transportation. The seas are also at the center of resource exploration that has expanded in scope over time.

During the colonial era and into our first century, fishing and whaling were major sources of national income. Since then, technological improvements have opened new doors, allowing the United States to access more of the resources found in the ocean’s previously impenetrable depths. Today, energy and mineral resource exploration operations are conducted far off the nation’s shores in exclusive economic zones, which represent 3.4 million square nautical miles of ocean space. Drilling and bottom mining rigs now routinely operate thousands of feet below the surface, taking the nation’s interests outward and downward with them.

In addition to new sources of resource wealth, the bottom of the ocean has become layered with “critical infrastructure.” The first transatlantic telegraph cable was laid between Ireland and Newfoundland in 1858, and others have followed. Today, nearly 99 percent of international data moves via underwater cables. Taken together, these cables are hundreds of thousands of miles long and lie in depths as deep as some of the planet’s tallest mountains are high. Resources such as oil, natural gas and minerals flow through a network of underwater pipes and pumping stations that crisscross the continental shelf. The production capacity of this infrastructure is significant. Offshore rigs generate around 1.8 million barrels of crude oil a day.

Perhaps the most obvious, yet least appreciated, national interest at sea is the United States’ duty to uphold its obligations to allies. The United States is a signatory to a series of treaties negotiated following the devastation of World War II. These treaties have bound our nation’s security to some fifty other sovereign states. The number and structure of these alliances are a great source of strength for the United States, conveying a mutual approach to security that neither the United States nor its allies need ever fear fighting alone. The president, as commander in chief, and the Department of Defense, with all of its component services, are required to perform all actions necessary to preserve the security of allied nations as if they were the sovereign territory of the United States itself. It is a heavy burden, but one made more difficult by the fact that, with the exception of Canada, every treaty partner lies across an ocean.

While the Air Force and some light Army airborne elements can get to Europe, the Middle East or Asia by air, most Marine Corps and Army components can only go by sea. Their Humvees, artillery, tanks and logistics trucks are simply too large and too heavy to be carried in sufficient quantities by air to be able to amass a credible combat force rapidly on another continent. To accomplish this task, the U.S. military’s Transportation Command retains a fleet of transport ships to carry division and corps-strength elements to distant locations within one to four weeks of activation. This type of operation was carried out in support of Operation Desert Shield/Desert Storm in 1990–91. Over a six-month period, Transportation Command assets were used to move over five hundred thousand troops and their equipment to Saudi Arabia to enable the removal of Iraqi forces from Kuwait. Conducting such an operation today, however, cannot be presumed with the same degree of anticipated success.

THE DESERT Storm campaign is a good point of departure to discuss emerging threats to America’s maritime interests. Allies, adversaries and certainly Iraqi leader Saddam Hussein were shocked by the speed and lethality of American forces. Many military analysts expected that the nearly 550,000 battle-hardened Iraqi soldiers would inflict significant U.S. casualties and prolong the ground war for months. Instead, U.S. forces suffered fewer than three hundred service deaths and quickly liberated Kuwait. The successful employment of new precision-guided weapons and an overwhelming hundred-hour ground offensive took center stage. These flashy components of the campaign, however, masked the American military’s continued dependence on unimpeded seaborne transport to move massive numbers of troops and equipment into large in-theater operating bases. Behind the scenes, nations such as Russia and China recognized how this dependence on access and freedom of movement could be a key vulnerability. Potential opponents know that deterring the American military’s projection of power requires restricting easy access to a combat theater and freedom of movement inside it. In other words, the lessons learned were to keep the Americans out and restrict their movement if they get in.

Following Desert Storm, both China and Russia began to put these lessons into practice by investing in “antiaccess/area-denial,” or “A2/AD” weapons, communications and intelligence systems. Primarily designed to deny access and freedom of movement, A2/AD systems have the ancillary effect of raising doubts in the minds of allies about the reliability of the American military in a crisis. Coming to the aid of an ally would mean having to brave highly lethal A2/AD weapons.

Chinese A2/AD modernization priorities include advanced mines, surface-to-air missiles, surface-to-surface missiles, stealth aircraft and antiship ballistic missiles. Two prominent examples are China’s “carrier killer” DF-21D and DF-26 ballistic missiles, both capable of long-range strikes and equipped with maneuverable warheads. Even more troubling is China’s development of hypersonic weapons—missiles that can fly five times the speed of sound and at altitudes low enough to avoid most missile defenses. Chinese carrier-killer, hypersonic and other sophisticated weapons systems will be “netted together” with intelligence, communications and fire-control networks.

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.

It is imperative that America’s fleet reach 355 ships within the next ten years. There is, in fact, a path to achieve this goal that is both achievable and affordable. Small investments now in ship maintenance and modernization could allow critical ships in the fleet to serve longer, notably among some advanced Aegis cruisers and nuclear fast-attack submarines. Additionally, there are some ships recently transferred to the inactive ready reserve force, also called the “ghost fleet,” that could be brought quickly back into our service rather than being transferred to the navies of foreign partners. Lastly, we can increase the new ship production rate on critical designs, such as the Virginia-class submarine, and accelerate the development of the Navy’s newest frigates, in order to bring these low-cost, multi-mission ships into the fleet in large numbers. The Navy has already begun this process by looking at mature foreign and domestic models, such as the Italian-designed FREMM and American-produced National Security Cutter, which have already been built and could easily be produced in numbers by American workers. These strategic approaches could convince both China and Russia that the United States is prepared to defend its interests at sea.

ALONE AMONG the services, the Navy is always deployed. In wartime, all of the services deploy. In peacetime, the Army and Air Force train and exercise but do not deploy persistently. However, the Navy, and its accompanying Marine Corps, deploy operationally twenty-four hours a day, seven days a week, 365 days a year—year in, year out, in peace and in war. This is because the very presence of naval forces demonstrates American interests without having to intrude on another nation’s sovereignty. Naval forces convey the relative importance of American interests through ratcheting up or down the number of ships in a given theater. The Navy’s unique “scalability,” along with its ability to arrive and stay, or to make its presence known and then quietly move on, gives our commander in chief military and diplomatic options.

America cannot retreat from the seas. Its maritime interests are enduring and growing. Great wealth in the form of food stocks, minerals and energy resources lies beneath the waves that find their way to our shores. Additionally, access to lines of communication via the swiftest and most efficient routes across international waters, as well as maritime linkages to forty-nine transoceanic treaty partners, are of critical interest to the United States.

The threat to those interests is growing. Despite a brief post–Cold War respite of calm seas, the maritime domain is once again seeing rough waters as an arena of economic, diplomatic and military competition. China, Russia and Iran have invested heavily in ways to keep the U.S. Navy out of critical maritime regions. They are increasingly challenging American maritime interests and finding no response. The inability to respond is driven by a collapse in the size of U.S. naval forces over the past quarter century. Our adversaries and potential opponents see all of this as an indicator of overall national decline and an invitation to assume a larger role upon the world’s oceans. They have just begun what ultimately could become a financially and strategically disastrous naval arms race in an attempt to overmatch U.S. forces in their regions.

But if the United States were to reverse course quickly on its own shipbuilding plans and pursue a 355-ship fleet within a decade, it would revitalize the Navy and safeguard American national interests.

Roger Wicker is a U.S. senator and chairman of the U.S. Senate Armed Services Subcommittee on Seapower. Dr. Jerry Hendrix is the director of the Defense Strategies and Assessments Program at the Center for a New American Security.