The U.S. has invested heavily in submarines for several purposes: to help sustain its nuclear deterrent, restrain an enemy from using its own nuclear-missile subs in a first strike, hunt down enemy attack subs (the best weapon to use against a submarine is another submarine), engage surface warships, strike land targets with conventional cruise missiles and even insert special forces and perform other clandestine acts, such as tapping undersea communications cables. The key to all these missions is the nuclear-powered submarine’s ability to remain submerged and out of sight for months at a time.
Tensions are rising globally, with Russia in Eastern Europe and China in East Asia making the prospect of a great-power war (or worse, wars) seem more possible now than at any time since the end of the Cold War. In particular, the efforts of the Chinese People’s Liberation Army (PLA) to prevent U.S. forces from interfering in the “Asian Mediterranean” have challenged the U.S. Navy’s historic Pacific dominance. The Communist Party of China’s confidence—and bellicosity—seem to be growing along with its capabilities in the region.
Submarines offer Western powers an option to engage a hostile power militarily without automatically setting the stage for a nuclear exchange. Moreover, submarines enable a state to fight the long war despite complications or even reversals in the theater of operations as defined by the aggressor. Submarines can even redefine the theater: Just because the enemy wants to constrain the fighting to an arena of its choosing doesn’t mean you have to accept that constraint.
However, in order to embrace the possibilities of submarine warfare, U.S. war planners have to look back at historical lessons and reevaluate legal restraints to use submarines most effectively by unleashing their greatest abilities: stealth, endurance and lethality.
Modern submarines have come full circle in the roles intended for them. The first generation of proper submersible warships that appeared during World War I were conceived as “fleet boats” to scout ahead of the main line of battleships and battlecruisers and maybe get in a lucky shot with a torpedo. Imperial Germany, finding itself distinctly outgunned on the high seas, turned to submarines as a strategic weapon to strangle Great Britain by destroying its merchant fleet. While effective—and controversial; unrestricted submarine warfare is one of the factors that brought the U.S. into World War I on the side of the Allies—the German submarines at the time could not inflict enough losses to outpace the ability of U.S. and U.K. shipbuilders to replace them.
Nazi Germany, again overpowered on the high seas, had relatively greater success in World War II, when its wolfpacks of capable submarines (commonly known as U-boats) were employed early as a means of blockading Britain. They managed to sink about 6,000 ships totaling 14 million tons, but this was still short of the requirements for victory. Despite their fearsome reputation and lethally dangerous technology and tactics, the U-boats were unable to paralyze cross-Atlantic shipping. Again, British and especially American shipbuilding easily replaced lost tonnage as the wolf packs were hunted to near extinction by Allied sub-killing ships and aircraft.
Much more effective and much less known were the operations of U.S. submarines against Japan during WWII. After the attack on Pearl Harbor and the loss of the Philippines, submarines were one of the few weapons America had in hand to strike back. Unlike the German operations, American submarines eventually did paralyze Japanese sea traffic almost completely, denying Japan access to vital resources that it theoretically possessed overseas but could not exploit because of the difficulty of transporting them to the home islands.
During the war, 263 U.S. submarines operating in the Pacific claimed 1,392 ships and nearly 5.6 million tons, which was enough to almost terminate delivery of various strategic goods, especially oil. While 1,154 German submarines destroyed almost three times more tonnage, they never approached the strategic effect achieved by American submarines, since Japan was unable to replace the cargo ships and tankers it lost.
While Axis and Allied submarines did manage to sink a number of enemy warships—sometimes quite spectacularly—the only potentially war-winning undersea operations were the Kriegsmarine and U.S. Navy campaigns against enemy merchant shipping, with the latter being decisive. Both of these efforts arguably violated various protocols and agreements pertaining to the sinking of unarmed merchant vessels dating back to before World War I and reiterated before the outbreak of WWII. By and large, these international rules said a warship, surface or submarine, was obliged to ensure the safety of passengers, crew and ship’s papers before sending a merchant ship to the bottom. Of course, neither the Japanese nor the Allies were disposed to cooperate with enemy submarines in this regard.
After WWII, the international rules governing the use of submarines in war were essentially renewed under the 1949 Geneva Convention with regard to what sorts of vessels are or are not legitimate targets and what are combatants’ responsibilities to search for survivors. Indeed, even the sinking of the Argentine navy cruiser General Belgrano by the nuclear attack submarine HMS Conqueror during the 1982 Falklands War was controversial because it occurred outside a U.K.-declared maritime exclusion zone that defined the warfighting area.
In December 1982, the UN adopted the United Nations Convention on the Law of the Sea. This agreement makes little mention of the rules of armed conflict, and none of submarine warfare. More guidance is provided by the 1949 Geneva Convention, which established a legal framework for the humane treatment and protection of victims of armed conflict at sea, the wounded, sick and shipwrecked. But submarine warfare rules are difficult to interpret from the various existing legal acts, and therefore they can be bent to the needs of the warfighting party.
It is doubtful that such rules and protocols will even be respected in the event of a great-power conflict with global implications. Yet the British government of Prime Minister Margret Thatcher was so stung by the criticism it received after the General Belgrano sinking that the Royal Navy moderated its submarine activity accordingly. But the incident also clearly demonstrated the ascendency of modern attack submarines against all manner of surface targets.
Submarines underwent rapid improvement during the Cold War, becoming longer-ranged, better-armed and a lot larger. The U.S. submarine fleet is divided into two major types: First is the nuclear ballistic missile submarine (SSBN) “boomer” or city killer, which is used only to provide global nuclear deterrence against any other nuclear power willing to attack U.S. territory. The U.S. Ohio-class SSBN is ten times the size of the WWII-era Gato-class deployed against Japan. The second type is the multirole submarine (SSN), officially designated as a fast-attack submarine, which is the size of a WWII light cruiser. (It should be noted that the “N” designation refers to the propulsion system, not the armament.)
The U.S. has 14 Ohio-class Trident II-armed SSBNs in service, forming one of the legs of America’s nuclear triad. Four other SSBNs have been converted to cruise-missile subs with a stock of 154 Tomahawk missiles designed to conduct conventional attacks against land targets. There are also three types of SSNs in service: 29 Los Angeles-class, 19 Virginia-class and three Seawolf-class SSNs on active duty, totaling 51 (although one Seawolf damaged in an accident in September may be scrapped). They are armed with guided torpedoes and non-nuclear missiles that can be launched from torpedo tubes. Virginia-class submarines have an additional 12 vertical launchers for Tomahawks.
The main task of the fast-attack submarines is to track and (if necessary) destroy enemy submarines, especially strategic missile submarines. U.S. or British SSNs continually shadow Russian and Chinese boomers to eliminate them quickly with guided torpedoes in the event of a major war, denying them the ability to launch their ballistic nuclear missiles.
The other task of fast-attack submarines is to conduct precision land attacks against a wide variety of targets, usually those with strategic value or related to air defense, to lead the way for airpower strikes in local, regional or even major conflicts. Since the 1991 Gulf War, 2,193 Tomahawks in total have been launched by the U.S. Navy against targets in Iraq, Afghanistan, Yugoslavia, Libya, the Islamic State and Syria. Many of them were launched from surface ships, but a considerable number were also launched from submarines. Submarines can approach to an enemy’s coast undetected and execute deep, precision land-attack strikes with deadly effect.
China’s PLA Navy also operates a large fleet of submarines of various types, including many modern vessels commissioned in the 21st century. Among them there are six SSBNs, six nuclear powered attack submarines and 46 conventionally powered attack submarines. The fleet also has three older nuclear-powered and 10 conventionally powered submarines in reserve, and China has an aggressive program for building new SSBN and SSN types.
Russia has fallen quite a way from the Soviet Union’s heights as a submarine power. Presently, the Russian submarine fleet consists of 46 active subs: 10 SSBN units; eight nuclear cruise-missile subs, seven SSNs and 21 conventionally powered subs. Russia’s plans to increase its submarine force have been hampered by accidents and lack of funds.
The U.K. and France also operate nuclear boomer and attack submarines. The boomers form part of the countries’ respective nuclear deterrents, and the attack subs might be expected to join a significant effort against a major power. In addition, France manufactures advanced non-nuclear attack submarines for export. A number of nations, such as Germany and Sweden, also manufacture advanced conventionally powered submarines. Such vessels are in service with many navies.
In Peril on the Sea
In evaluating how valuable submarines would be to the West in battling belligerent great powers, it is best to focus on the nuclear-attack submarine, which possesses the endurance, stealth and armament to conduct the long war. Besides, if boomers ever come into play, all bets are off because of the massive scale of potential destruction.
Operators of nuclear attack submarines can conduct missions on a global basis. There is no sea or region beyond their reach, with the important exception of brown-water littoral regions where the waters are too shallow to risk them except on the most clandestine activities. The SSN wants deep water and expanse in which to maneuver and hide.
An important advantage in warfare is the ability to destroy, or at least threaten, things of value outside the area an enemy is physically able to protect. In the case of China—and, to a much lesser extent, Russia—one such thing of value is the open seas through which trade occurs and money is generated. China, in particular, would be doomed if its maritime traffic—imports and exports—were to be interrupted. Cognizant of this fact, China has embarked on its One Belt, One Road initiative in part to enable a land network through Eurasia for importing raw materials and exporting manufactured goods, without having to expose its commerce to the U.S. Navy.
But achieving that goal is a long way off for China, and the Communist Party seems to want Taiwan sooner rather than later. Even if China were successful in an invasion of Taiwan, submarines would enable the U.S. and its suitably equipped allies to continue the long war to the detriment of China’s economy and long-term prospects.
While U.S. and allied surface naval capabilities, as they stand, remain superior to any adversary, or indeed, any combination of adversaries, these cannot necessarily be counted on to continue the long war on their own. First, they may be required to defend home waters. Second, China or Russia could degrade, if not eliminate, the space-based reconnaissance and navigational assets on which Western surface navies rely to conduct operations. Chinese and even Russian anti-satellite capabilities are possibly well in advance of deployed U.S. technologies in this area. It will be interesting (not in a good way) to see how the U.S. risks its carrier task forces in seas without satellite coverage.
At the same time, submarines are inveterate hunter-killers, capable of patrolling an area and detecting and engaging targets without direction or even communication with friendly bases. While warfighting doctrine and technology make them more effective with such interaction, they are also trained to operate alone. It is possible even today for a U.S. Navy SSN to be ordered into an area and prevent all enemy shipping without any further instructions along the way.
Much of China’s foreign trade, which is of enormous volume, goes by sea. Shanghai alone handles more than 500 million tons annually, making it the busiest port in the world. However, a naval blockade against China is difficult to execute due to the long coastal lines and efforts the PLA has invested in controlling its regional approaches with a bristling array of weapons. The Third Reich faced a similarly difficult nut to crack in Great Britain. The United States was denuded of many of its front-line weapons by the Japanese attack on Pearl Harbor and related offensives. In all these cases, submarine warfare helped, or could help, significantly disrupt the enemy’s foreign trade.
If the U.S. were unable to compete in a certain theater or even faced short-term defeat and catastrophe, nuclear attack submarines would offer the opportunity to carry on and inflict harm on the enemy while the smoke clears and the bandages are applied. Great powers pioneered the concept of the extended blockade—a blockade of intent rather than exclusion zone—going back to the wars in the Age of Enlightenment. If you control the seas, use that control to prevent any ship anywhere in the world from reaching your enemy.
Modern U.S. submarines can act today in the same way against any enemy as they did against Japan in WWII. They could execute a complete naval extended blockade by denying delivery of supplies via sea from wherever they originate without even approaching enemy ports. Moreover, guided torpedoes and anti-ship missiles can reliably destroy targets from ranges and engagement angles that submariners of previous generations would have found impossible.
The main constraints, then, on a modern submarine commander to eliminate enemy merchant ships and thereby throttle or at least diminish the enemy economy are the rules observed by the commander’s home country. According to the 1949 Geneva Convention, any cargo conveyor—land, sea or air—should be warned before an attack to enable it to turn away from its destination. Then, in the case of a merchant ship, if it does not follow such a warning, time should be allowed to enable the noncombatant crew to evacuate. Only then would the ship be considered a legitimate military target.
The problem is that making such a warning would immediately betray the submarine’s location, thereby compromising its key advantage as a weapon of the long war. The Germans faced this problem in two world wars. The Americans faced it in the second, and they may face it again.
Violating the Geneva Convention when it comes to destroying merchant shipping would undermine the very world order the U.S. is fighting to protect. On the other hand, what if the enemy were counting on America’s observance of that world order, and planning to use it against the U.S. in order to erect its own? It may be time to reevaluate the international rules that have governed warfare since the middle of the last century.