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The submarine has the smallest value of any naval vessel for the direct attack upon trade. She does not carry a crew that is capable of taking charge of a prize: she cannot remove passengers and other persons if she wishes to sink one.

— Alfred Thayer Mahan

The Influence of Sea Power upon History, 1660-1783

If the United States were to become engaged in international armed conflict with the People’s Republic of China (PRC), the National Command Authority might issue the order, “Execute unrestricted submarine warfare,” as they did at the onset of World War II. The thesis of this paper is the answer to the question that a future Joint Task Force (JTF) Commander charged with defending Taiwan against the PRC might one day ask in regard to Chinese merchant shipping,2 “Can I kill them with my subs?” In short the answer is: yes it is acceptable under the U.S. interpretation of international law, but it will not likely be authorized by the rules of engagement. This is why.

Notional Scenario
In a fictitious scenario built by the Joint Military Operations Department of the Naval War College in December 2006, the United States is called upon to defend Taiwan against aggression from the PRC. In the scenario, relations between the PRC and Taiwan have strained, and Taiwan elected a pro-independence president who proposed Taiwan’s admission to the United Nations. The PRC conducted large scale missile, naval, amphibious and air exercises, with missiles fired in the vicinity of Kaohsiung, Taiwan. Unification talks were started, but soon broke down completely. Eventually, the PRC seized and occupied Quemoy Island with significant PRC and Taiwan losses. The United Nations resuscitated talks between the two parties, but these soon broke down as well. World reaction was generally muted, as many countries saw the matter as an internal conflict. Eventually, the PRC built up amphibious forces opposite Matsu Islands/ the U.S. conducted non-combatant evacuation operations, and Taiwan mobilized its reserve forces. Taiwan asked for U.S. assistance in its defense and the United States responded by establishing a coalition to defend Taiwan and deter PRC aggression. One issue raised by this scenario is: Would unrestricted submarine warfare against PRC merchant vessels be legal during the operation?

This paper will first provide a brief analysis of the law governing the attack of enemy merchant shipping. It will show that submarine warfare against enemy merchant shipping is within the bounds of lawful conduct. However, that judgment is based on an expansive view of customary international law. The United States holds this view even though most of the rest of the countries of the world, including many of our allies, do not. Second, this paper will discuss briefly the history of unrestricted submarine warfare with particular attention toward interdiction of enemy merchant shipping. The point of this section of the paper is to show that belligerents in the 201 h century generally recognized that unrestricted submarine warfare was on the edge of lawful conduct and perhaps even unlawful. It will further show that submarine warfare has historically played a disproportionate role in influencing policy makers. This paper will conclude that even though attacking enemy merchant shipping in certain circumstances is considered lawful, it should not be authorized under the rules of engagement (ROE) because such actions would significantly reduce the legitimacy of U.S. operations. Operations that lack legitimacy undermine U.S. efforts.

Interdiction of Enemy Merchants Shipping
Under International Law Many fault lines in the law of war have been addressed in recent literature.6 One such fault line that has not received that much attention is the attack on enemy merchant shipping by submarines. According to the U.S. Navy Commander’s Handbook on the Law of Naval Warfare, the “rules of naval warfare pertaining to submarine operations against enemy merchant shipping constitute one of the least developed areas of the law of armed conflict.”

Are enemy merchant vessels lawful targets? First of all, in order for an object to be lawfully targeted, it must be a military objective and not a civilian object. According to the 1977 Additional Protocol I (API) to the 1949 Geneva Conventions, in “order to ensure respect for and protection of civilian population and civilian objects, the Parties to the conflict shall at all times distinguish between the civilian population and combatants and between civilian objects and military objectives …. ” The Commander’s Handbook states that civilian “objects consist of all civilian property and activities other than those used to support or sustain the enemy’s war-fighting capability.” Furthermore, the API requires that the warring parties “shall direct their operations only against military objectives.” The API provides further relevant prohibitions. Under Article 51, “Civilian objects shall not be the object of attack,” and the “civilian population as such, as well as individual civilians, shall not be the object of attack.”

The API defines civilian objects as “all objects which are not military objectives.” The crux of the matter is whether PRC merchant vessels are military objectives, since only military objectives may be attacked. What are military objectives? This is not an easy question to answer and even the drafters of the API noted that the API text “certainly constitutes a valuable guide, but it will not always be easy to interpret, particularly for those who have to decide about an attack and on the means and methods to be used.” Indeed, under the API military objectives are “limited to those objects which by their nature,’ location, purpose,’ or use make an effective contribution to military action and whose total or partial destruction, capture or neutralization, in the circumstances ruling at the time, offers a definite military advantage.”

Interpreting this article broadly, the Commander’s Handbook states that military objectives include “economic targets of the enemy that indirectly but effectively support and sustain the enemy ‘s war-fighting capability [and] may also be attacked.”20 The United States considers this customary international law’ and the Commander’s Handbook refers to the destruction of Confederate cotton within the South by Union forces as an example of justified targeting of economic objects.

On the other hand, a more restrictive reading of this article focuses on the plain meaning of the phrases, make an effective contribution to military action and offers a definite military advantage. This interpretation would require that “there … be a definite military advantage for every military objective that is attacked”23-a closer link between the object and the conflict. Many states-including most of our allies-have moved to the more restrictive interpretation. The U.S. is one of the few holdouts of the expansive view of military objective.

Additionally an attack must apply the rule of proportionality. The Commander’s Handbook states that “it is not unlawful to cause incidental injury to civilians, or collateral damage to civilian objects, during an attack upon a legitimate military objective” but that injury or damage “must not be excessive in light of the military advantage anticipated by the attack.”

An additional complication in this calculation, as one noted legal scholar recognized, is “whether it is permissible to take own-forces survival into consideration when deciding if, when, and how attacks may be mounted.” Although the London Protocol does not allow for this, the Commander’s Handbook does. The London Protocol “makes no distinction between submarines and surf ace warships with respect to attacks upon enemy merchant shipping. “26 It requires that submarines must first safeguard passengers and crews of enemy merchant ships before an attack, except in cases where a ship persistently refuses to stop after having been ordered to do so. This requirement is more restrictive than the one imposed by the Commander’s Handbook. U.S. Navy doctrine reflects this view.

According to the Commander’s Handbook, the basis of the law governing submarine interdiction of enemy merchant shipping is the London Protocol of 1936 “coupled with the customary practice of belligerents during and following World War II (emphasis added).”27 The customary practices of belligerents regarding submarine warfare in the Second World War were not in keeping with the London Protocol. Disregard for treaty obligations weakens the treaty.

The Commander’s Handbook states that commanders must “take all reasonable precautions … to keep civilian casualties and damage to the minimum consistent with mission accomplishment and the security of the force. “28 Searching for and collecting the wounded, shipwrecked and sick following an engagement may subject submarines to undue hazard. The legal requirement for submarines as set forth by the Commander’s Handbook is: as .. far as military exigencies permit, after each engagement all possible measures should be taken without delay to search for and collect the shipwrecked, wounded, and sick and to recover the dead.” 29 If military exigencies do not permit such efforts, submarines are required to pass the “location of possible survivors to a surface ship, aircraft or shore facility capable of rendering assistance.”

All of the above requirements are imposed on submarines interdicting enemy merchant vessels unless one of the following seven requirements is met.

  1. The “enemy merchant vessel persistently refuses to stop when” ordered to do so; or
  2. It “actively resists visit and search or capture;” or
  3. The enemy merchant vessel “is sailing under convoy of enemy warships or enemy military aircraft;” or
  4. It “is armed;” or
  5. It “is incorporated into, or is assisting in any way the enemy’s military intelligence system;” or
  6. It “is acting in any capacity as a naval or military auxiliary to an enemy’s armed forces” or
  7. The “enemy has integrated its merchant shipping into its war-fighting/war sustaining effort and compliance with the London Protocol of 1936 would, under the circumstances of the specific encounter, subject the submarine to imminent danger or would othenwise preclude mission accomplishment. “

These first two requirements are not remarkable in that they mirror the language set forth in the London Protocol. The last requirement is the most troubling. It is an exception that swallows the rule. A reasonable interpretation of the last requirement (for the purposes of this paper, “the military exigency exception”) would allow submarines to attack enemy merchant vessels without warning and without safeguarding the crews and passengers. The second and third order effects of this rule are daunting.

Unrestricted Submarine Warfare: a Brief Historical Analysis
Submarine attacks are brutal, and thus provoke a response that is disproportionate to the actual damage done by a submarine attack. Time after time, throughout history, despite knowing that the use of submarines to attack enemy merchant shipping would be at best legally questionable, belligerents did so anyway and usually paid a dear price politically.

When the First World War started, Germany at first “fastidiously observed the international rules of engagement.” When they encountered enemy merchant shipping, they removed the passengers and crews of intercepted crafts even though the rules when they were written were intended for surface ships and not submarines. At the onset of the war, both sides focused their submarine efforts not on commerce raiding, but rather on their role as warships to be put into action against other warships. Two factors contributed to Germany’s retreat from this position: one, the U-boat had sharp limitations as a warship against the British; and two, merchant shipping constituted the lifeblood of Britain.34 In October 1914, a first was recorded in history when a German submarine, without warning, fired one torpedo at an unarmed French merchant vessel, the Amiral Gentaume, not sinking her, but still causing the loss of over forty passengers.

Despite early intentions to the contrary, the debate in Germany quickly evolved from whether to conduct operations against British shipping to how these operations were going to be accomplished. It was presumed that because there was no accepted international law governing submarines, if submarines engaged in attacks on merchant vessels, they must operate under the rules governing surface ships.37 The closest thing to such rules during the World War I (WW I) era was the Declaration of London of 1909.

In November, Germany declared that “every enemy merchantman encountered would be sunk and that the navy could not in every case assure the safety of the passengers and crew.” Germany’s justification was that this measure was in retaliation for the illegal British effort to essentially starve the German people. The U.S. responded sternly to Germany, stating there would be serious consequences if a submarine destroyed an American vessel or killed American citizens. In May, a German U-boat sunk the LUSITANIA, which Germany considered a valid target as outlined by Germany’s November declaration Over 100 American citizens were killed.” Many Americans felt that Germany’s adoption of submarine commerce raiding proved the Germans to be ruthless, uncivilized war makers.” Sinking unarmed merchant ships without challenge or any means of saving the crew and passengers went beyond the pale and put the issue of unrestricted submarine warfare “back into the political arena.”

American outrage at the sinking of the LUSITANIA caused Germany to operate under more restrictive rules of engagement through the rest of 1915 and all of 1916.” These restrictions seemed impossible to achieve and required submarine commanders to ascertain whether a target was neutral, enemy, merchant, or passenger-armed or unarmed- before firing a torpedo.” These carefully calibrated rules revealed the policy and legal sensitivities inherent in the interdiction of merchant vessels. This policy was abandoned in February 191748 which eventually caused the United States to sever relations with Germany. One month later, four U.S. merchant ships were sunk, with about 15 killed. America had had enough; President Wilson called for a congressional declaration of war against Germany.

As a testament to the disproportionate power that submarines have on policy makers, “a handful of U-boats, craft that had received little attention just three years earlier at the outbreak of hostilities, had performed what amounted to an unintentional miracle, the greatest political feat of the war. “49 As one author put it, “Germany’s decision to employ U-boats as commerce raiders must rank as the most important event in the First World War- by far.” so That decision “ended once and for all the distinction between combatant and civilian” in “warfare between civilized states.” Germany’s policy of attempting to bring down Britain by destroying her industrial capacity via unrestricted submarine warfare “came within a whisker of success, but in the end proved ruinous to the German cause because it was instrumental in bringing the United States into the war on the Allied side.”

After the war Britain pressed for a total ban on submarines, while the rest of the great powers sought to provide a legal framework for submarine warfare. In the 1930’s the London Protocol was negotiated among all the major powers including Britain, German and the U.S. In short, the London Protocol required submarines to act within the same rules as surface warships. Just as submarine warfare had inadvertently changed the course of WW I, the first submarine sinking of a merchant vessel in WW II was a mistake. Hitler had decreed that submarines would conduct themselves in accordance with the London Protocol: “no U-boat should attack any merchant ship without first challenging her and making sure that her passengers and crew” were safe.H Yet on 3 September 1939- the date Britain declared war on Germany-a German submarine sunk a large British passenger liner, the A THENIA, without warning, but did not report the sinking to higher headquarters because of Hitler’s earlier decree. Though Germany denied responsibility for the sinking, they did so in all honesty because the submarine commander still had not reported the incident out of fear of Hitler. Hitler reemphasized his intention to his navy. He issued an order that “on no account are operations to be carried out against passenger steamers, even when under escort.” The poor results from this period of submarine warfare “confirmed what was known from the First World War: submarines make little impression on commerce unless they are employed with a ruthless disregard for the accepted rules of warfare.”

Although Hitler had forbidden unrestricted submarine warfare on merchant shipping at the outset of hostilities, Admiral Karl Doenitz, Germany’s chief naval officer, knew that Germany would have to resort to such a policy in order to win the war, treaty obligations aside. Doenitz recalled, “One after the other the restrictions came off.” At one point, Doenitz ordered that “all attempts to rescue the crews of sunken ships will cease ….” The justifications for such orders were numerous: reprisal to a foe’s unlawful wartime acts; necessary because merchant ships were armed and dangerous to submarines; and the general integration of merchant shipping into an enemy’s war fighting capabilities. As soon as America and Germany had declared war on one another, German submarines quickly produced unprecedented success against U.S. merchant vessels.

In the Pacific, America pushed its treaty obligations aside immediately. On 7 December, still reeling from the shock of the attacks on Pearl Harbor, American submarines received a message from the Chief of Naval Operations, Admiral Stark: “execute unrestricted submarine warfare against Japan. There was no debate, no hesitation, and no great concern from the national leadership about this policy. Germany had attempted to limit unrestricted submarine warfare. Unrestricted submarine warfare had forced President Wilson, a reluctant warrior, to enter WW I. Yet in 1941 within hours of attack, the United States had a policy of unrestricted submarine warfare, in violation of its London Protocol obligations. Why was this an easy step for the United States to take?

During the interwar period, the U.S. Navy had seen Japan as a potential foe and American submariners saw their purpose as “to scout for the enemy battle fleet and to attack the enemy’s capital ships.” Yet the decision to order unrestricted submarine warfare did not come as a surprise, despite the United States’ treaty obligations and despite the notion that such tactics were scorned by most naval officers who were taught, as Mahan preached, that commerce raiding was “the tool of the weaker power in a conflict.” Everybody understood “that a directive for unrestricted submarine warfare could be expected within the first week after the outbreak of hostilities.”

There are several legal conclusions this paper draws. The United States has adopted a liberal interpretation of “military objective” under customary international law. That interpretation represents an expansive view of the law and is one that is specifically not shared with most of the rest of the countries in the world including most of our allies. The United States is practically alone in this view of the governing law.

Enemy merchant ships fall within the definition of military objective under this broad interpretation of customary international law. Assuming that enemy merchant ships are considered military objectives, the rule of proportionality still applies when interdicting enemy merchant shipping.

Although not allowed under the London Protocol, the Commander’s Handbook permits taking survival of one’s own forces’ into consideration in the interdiction of enemy merchant shipping by submarines. In other words, if military exigencies do not permit, submarines are not required to safeguard the crews of enemy merchant ships before an attack, according to the Commander’s Handbook. Specifically, if the enemy has integrated its merchant shipping into its war-fighting and war sustaining effort and compliance with the London Protocol would, under the circumstances of the specific encounter, subject the submarine to imminent danger or would otherwise preclude mission accomplishment, then a submarine may attack Chinese merchant shipping without warning and without providing for the safety of its crews. This military exigency exception to the London Protocol is an exception that swallows the rule. By way of analogy, imagine if U.S. ground forces were taught that they must obey the laws of land warfare, except if compliance would preclude mission accomplishment. Such illogic would eviscerate the rules.

We can reach at least two conclusions based on a brief analysis of submarine warfare during the First World War. First, unrestricted submarine warfare was so lethal that no nation whose existence depended on overseas trade could be counted on to refrain from unrestricted submarine warfare. Germany nearly succeeded in bringing down Britain by destroying her ability to conduct overseas commerce. Second, unrestricted submarine warfare had powerful and disproportionate political ramifications. Germany’s sinking of unarmed merchant ships without challenge or any means of saving the crew and passengers went beyond the pale in the opinion of the international community and caused the U.S. to enter the war against Germany.

A brief historical analysis of World War II also provides several insights. When Hitler decreed that no German U-boat should attack any merchant ship without first challenging her and making sure that her passengers and crew were safe, he essentially eviscerated the submarines’ ability to remain undetected. As a direct result, their effectiveness decreased dramatically. As these restrictions were lifted one by one, German submarines became more effective. On the other hand, American submarines in the Pacific in World War II demonstrated just how effective submarines could be if they operated under unrestricted rules of engagement. It is likely that a future JTF Commander will therefore see the need to operate his submarines in a manner in which they remain undetected in order to maximize their effectiveness.

Another insight from a historical perspective is that in order to be effective, submarines must remain undetected. This means they cannot issue warnings and provide for the safety of the crews prior to firing a torpedo. In the Second World War the belligerents believed that it was inevitable that restrictions on submarine warfare would fall as the belligerents attempted to counter each others unlawful wartime acts or respond to a military exigency. The practices of belligerents with regard to submarine warfare in the Second World War were not in accord with the London Protocol.

Finally, this paper offers three points for consideration to the future JTF Commander faced with the possibility of waging unrestricted submarine warfare against Chinese merchant shipping. A policy of unrestricted submarine warfare against enemy merchant vessels must come from the National Command Authority. Attacks may even be planned and approved at the strategic level in order to achieve strategic objectives. A JTF Commander may have little advance notice. As we saw during World War II, the order to Execute unrestricted submarine warfare came down from Washington, D.C. within six hours of the surprise attacks on Pearl Harbor. A JTF Commander must therefore be prepared to provide input on this issue to his higher operational commanders and the strategic commanders at a moment’s notice.

Additionally, a JTF Commander must understand the legal parameters in which he or she operates. This paper delineates some of those legal parameters. Unarmed enemy merchant vessels will be seen as proper military objectives by a JTF Commander in the future under a reasonable interpretation of the rules set forth in the Commander’s Handbook. The JTF Commander must realize though, that the Commander’s Handbook provides an expansive interpretation of military objective under international law. It is one that the U.S. has adopted, but one that most of the other nations of the world have rejected. The U.S. is one of the few holdouts in this regard Finally, sinking unarmed merchant ships without warning or any means of saving the crew and passengers will be viewed internationally as beyond the pale. The international community will see such action as outside of the rules set forth by customary international law. After all, the U.S. interpretation of the requirements of international law is diametrically opposed to that of most of the rest of the global community. Before a future JTF Commander invokes the military exigency exception to compliance with the London Protocol in order to rationalize why his submarines were required to attack without first safeguarding the crews and passengers of unarmed enemy merchant vessels, he should carefully consider the damage such operations will do to the legitimacy of the overall operation. The courses of action the JTF Commander considers must be acceptable.

Accordingly, the legitimacy of an operation is at risk if the operation relies on a legal position that is not shared by most of the rest of the world. Domestic and international legitimacy is crucial to the success of an operation. Legitimacy concerns require that our operations “foster, sustain and communicate the legal, moral, and just nature of the operation and actions of the U.S. Government.. .. “64 Unfortunately, this broad interpretation of international law, if operationalized, would be counterproductive to U.S. efforts because it would diminish the legitimacy of U.S. efforts. Courses of action that are not characterized by legitimacy are not acceptable.

Admiral Doenitz’s words ring true today: Germany “adhered to the provisions of international law contained in the London agreement and that it was only step by step, in response to breaches of these provisions by the enemy that we allowed ourselves more and more latitude until finally we reached the stage as, it was inevitable that we would, where the London agreement was abandoned completely and for good.” The Commander’s Handbook provides exceptions to the London Protocol that threaten to swallow the rule and, if followed, endanger the legitimacy of future U.S. actions internationally.

As noted by Mahan at the start of this paper, “The submarine has the smallest value of any naval vessel for the direct attack upon trade” because “she cannot remove passengers and other persons if she wishes to sink one.” Since a submarine cannot effectively attack enemy merchant vessels while complying with the London Protocol, Mahan rightly saw this method and means of warfare as beyond the pale, and one that would severely jeopardize the legitimacy of the cause.

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