An Era of ‘Submarine Diplomacy’?

An Era of ‘Submarine Diplomacy’?

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There is a concept that has come to be known as “bomber diplomacy,” in which the United States uses its strategic bombers as a broader foreign and security policy tool. It has become a common sight in international skies to see B-52 and B-1 bombers, often flying together with allied jet fighters, sending strategic messages of deterrence to China and North Korea in Asia or to Russia in Europe. The flights are also thought to be an effective tool in reassuring U.S. allies in both theaters.

This deterrence, or reassurance, is achieved by raising the visibility of the bombers. Now, nuclear submarines – the ones that carry nuclear-armed ballistic missiles (SSBNs) – seem to be entering the same business, in what we might call “submarine diplomacy.”

The advent of submarine diplomacy is remarkable given that submarines are not meant to be visible. Submarine operations have long been called the “silent service.” Because of its invisibility, the submarine fleet is highly survivable, giving it assured second strike or retaliation capability. Once it becomes visible, adversaries know where you are, making you vulnerable and undermining their value as a deterrent. However, this traditional thinking appears to be becoming obsolete.

Vice Admiral Jeffrey Jablon, commander of the Submarine Force, US Pacific Fleet (SUBPAC) has been quoted as saying, “I would no longer characterize ourselves as a silent service. Deterrence is a major mission for the submarine force. You can’t have a credible deterrent without communicating your capabilities; if the adversary doesn’t know anything about that specific deterrent, it’s not a deterrent.”

In April 2023, United States and the Republic of Korea (ROK) singed a new document called the “Washington Declaration,” in which the U.S. is committed to “further enhance the regular visibility of strategic assets to the Korean Peninsula, as evidenced by the upcoming visit of a U.S. nuclear ballistic missile submarine to the ROK, and will expand and deepen coordination between our militaries.”

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It is notable that the document literally speaks only of “the upcoming visit” singular, arguably suggesting the reluctance of Washington to commit to the periodic deployments that many press reports suggested. Nonetheless, it seems wrong to conclude that this will be a one-off event. Along with the decision to establish a new body between the two countries, called the “nuclear consultative group (NCG)” – ostensibly echoing NATO’s “nuclear planning group (NPG)” – the idea of getting an SSBN to South Korea is seen as a new reassurance measure that Seoul managed to get from the U.S. In exchange, South Korea needed to reiterate its commitment to the nuclear non-proliferation treaty (NPT).

However, this is not quite an entirely new idea, as it had previously appeared in the Nuclear Posture Review (NPR), released in October 2022. That document stated that “We will work with Allies and partners to identify opportunities to increase the visibility of U.S. strategic assets to the [Indo-Pacific] region as a demonstration of U.S. resolve and commitment, including ballistic missile submarine port visits and strategic bomber missions.”

While this sentence did not get much attention when the NPR was published, the U.S.-Korea agreement can be understood in this context, and also in light of the words of Vice Adm. Jablon. In addition, one could argue that SSBN port visits in the ROK were not something that Seoul had to fight hard to secure in the run-up to President Yoon Suk Yeol’s state visit to the U.S, as Washington had already been willing to do it at least as early as the fall of 2022. In other words, it is inconceivable that the U.S. would be prepared to let other countries influence its SSBN operations without Washington’s active willingness.

That said, one of the most significant differences between bombers and submarines for the purpose of reassurance is that while at port, the SSBN cannot fulfill its deterrence mission, meaning that port visits could undermine the U.S. deterrent in military terms. Strategic bombers, too, cannot function while on the ground, but they cannot be in the air indefinitely, whereas nuclear submarines can remain underwater for extended periods of time. Quick deployments are part of the bombers’ mission. Moreover, whereas strategic bombers do not carry nuclear weapons for such deployments, SSBNs are believed to be carrying nuclear-armed ballistic missiles even during times of peace, for deterrence.

There is also a risk in allowing adversaries to detect the whereabout of America’s SSBNs, particularly following a port visit outside the U.S. The U.S. conducts tailored special operations to protect departing SSBNs, for instance using military dolphins as well as attack submarines and surveillance aircraft to detect adversaries’ submarines in and around Kings Bay Naval Submarine Base in Georgia, one of the main SSBN bases in the U.S.

In deciding to make use of its SSBNs for reassurance purposes, it is surely safe to assume that the U.S. government has thought through all the possible operational and other costs and risks. It is perhaps for this reason that Washington will not say anything about the frequency of SSBN port visits in Asia. Only when the subs are available and will the port visits are possible will they take place; perhaps once every few years, or even less frequently.

Still, it is now clear that the U.S. is willing to use its SSBNs for reassurance purposes, making them visible, as opposed to keeping them invisible. This reflects the increasing necessity of reassuring U.S. allies in the Indo-Pacific; in other words, the declining confidence that regional allies have in the credibility of U.S. extended deterrence. This applies first and foremost to South Korea. Yet Tokyo is also closely watching what the U.S. and South Korea are doing to enhance the credibility of extended nuclear deterrence, including the SSBN port visits, even though hosting SSBN visits would be virtually impossible for Japan given its strict “three non-nuclear principles” of not possessing, not producing and not permitting the introduction of nuclear weapons.

As this submarine diplomacy gets underway, Washington will need to come up with a clear set of goals that SSBN port visits are meant to achieve, in light of the advantages and disadvantages compared with strategic bomber deployments. Otherwise, submarine diplomacy will remain merely symbolic and the U.S. could end up wasting precious strategic assets. Given that SSBNs do not need to come to waters close to China, as the range of the Trident II (D5) missiles these boats carry is around 4,000 miles, it is difficult to justify port calls in the western Pacific in purely military terms. Meanwhile, as long as South Koreans are satisfied with SSBN port visits, the reassurance purposes are apparently met, meaning that the long-standing dilemma between deterrence and reassurance is set to play out yet again.

Michito Tsuruoka is an Associate Professor at Keio University and a Visiting Fellow at the Australian National University (ANU), 2023-2024.

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