Overview of the Submarine Proliferation Resource Collection

The NTI Submarine Proliferation Resource Collection details the submarine capabilities and import/export behavior of several representative countries around the world. The collection focuses on technological improvements to global submarine fleets, such as the spread of nuclear propulsion and Air Independent Propulsion (AIP) technologies, which increase the capability of submarines to deliver weapons of mass destruction (WMD). Additionally, the collection tracks conventional submarine proliferation in potential global flashpoints, particularly the Middle East, South Asia, and Southeast Asia.

Submarine proliferation impacts both regional stability and the ability of states to deliver WMD. Since the end of the Cold War, the total number of active submarines in the world has fallen, largely as a result of large-scale decommissioning of former Soviet vessels. ¹ However, the number of countries operating submarines has increased, due largely to ongoing regional tensions in the Middle East, South Asia, and East Asia. Countries that seek to acquire submarines can rely on a competitive global export market, which is only lightly regulated by international export controls.

Although the number of states acquiring submarines has grown in recent decades, the group of countries exporting submarines has remained relatively small. Today, France, Germany and Russia are the three most active exporters of conventional submarines. Between them, they have exported to more than 20 navies. ² China has concluded submarine deals with countries such as Pakistan, Thailand, and Bangladesh, and appears to have greater aspirations in the export market. ³ South Korea has also entered the submarine export market, delivering its first Daewoo-built attack submarines to the Indonesian Navy in 2016. ⁴

Competition among exporters for lucrative construction contracts can be fierce, and this has often led to producers offering technology transfer to secure deals. One example is France’s production technology transfer to Brazil as part of its 2008 sale of Scorpène-class vessels. ⁵ Technology transfers of this kind will likely result in the proliferation of submarine producers as recipients become capable of constructing their own submarines.

AIP Technology

Air Independent Propulsion (AIP) technology provides diesel-powered submarines with greater submerged endurance (several weeks as opposed to several days), thereby enhancing survivability. ⁶ This is achieved through the use of liquid or compressed oxygen or hydrogen fuel cells that allow vessels to stay submerged for longer periods without surfacing. ⁷ AIP vessels are smaller than nuclear powered submarines, giving them greater access to shallow, littoral waters. For nations that are unable or unwilling to develop nuclear powered submarines, AIP offers an attractive alternative that improves submarine performance without the financial or political costs of nuclear propulsion.

Implications for Regional Stability

New capabilities for conventionally-powered submarines, such as AIP technology and cruise and ballistic missile delivery systems, have heightened concern that nuclear armed states outside the Treaty on the Non-Proliferation of Nuclear Weapons (NPT), such as Israel, India, and Pakistan, could mount nuclear warheads on submarine launched delivery systems. ⁸ Taking the example of the NPT-recognized nuclear weapon states, non-NPT nuclear weapon states hope to ensure the survival of their nuclear deterrent in the event of attack. Although such sea-based deployments may increase stability by ensuring a second-strike capability, they also have the potential to trigger arms races that create greater instability. Additionally, some experts are concerned that mounting nuclear weapons on submarines increases their vulnerability to unauthorized use or terrorist attack, and that states may lack sufficient command—and—control to reliably manage a submarine—based nuclear force. ⁹ The proliferation of conventional submarines, even among states that do not possess a nuclear weapons capability, may also precipitate regional arms races, especially in the Middle East and East Asia.

Nuclear Propulsion

Despite the advent of AIP technology, a number of states continue to pursue nuclear propulsion, often for reasons of national prestige or arms race dynamics. India and Brazil have taken significant steps toward this goal. After years of research and development, India officially commissioned its first nuclear-powered ballistic missile submarine, the INS Arinhart, in August 2016. ¹⁰ India has also leased a nuclear-powered attack submarine, the INS Chakra, from Russia. ¹¹ By comparison, the development of Brazil’s nuclear-powered submarine lags far behind. ¹² In their bids to develop nuclear propulsion, both India and Brazil have received assistance from other states. Russia has been India’s key partner, while France is assisting Brazil in constructing the hull for its first nuclear vessel.¹³

In 2023, the United States and United Kingdom agreed to equip Australia with nuclear-powered attack submarines (SSNs) to address perceived threats from China. The agreement included the U.S. sale of 3-5 Virginia-class SSNs, co-development by the UK and Australia of a new SSN, and a pledge by all three countries to expand their combined submarine industrial base. ¹⁴

Any spread of naval nuclear technology creates proliferation concerns due to a loophole in the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). The naval nuclear propulsion loophole allows states to withdraw fissile material from international safeguards if it is to be used for military reactor fuel, thus creating the possibility that fissile material could be diverted to a nuclear weapons program. ¹⁵

When considering the export of submarines, states often prioritize financial gain over security concerns because of the lucrative nature of construction contracts. Russia’s provision of nuclear reactor and submarine-design technology to China and India are examples of this phenomenon. ¹⁶ Additionally, multilateral export control regimes contain few restrictions on the sale of submarines, partly because they have historically been used for defensive purposes. The UN Arms Register requires states to declare the transfer of warships that displace 500 metric tons, or are able to fire missiles or torpedoes with a range of 25 kilometers or more. ¹⁷ The Wassenaar Arrangement goes further by requiring states to report the sale of vessels that displace 150 tons, as well as those that are equipped to fire missiles or torpedoes with a range of 25 kilometers. ¹⁸ However, declarations to the United Nations have not been comprehensive, and neither of these regimes bans the sale of any type of submarine. ¹⁹ The NPT also allows the export of nuclear submarines, as nuclear propulsion is viewed as an acceptable use of nuclear energy. As a result, there is little to prevent states from selling submarines to countries located in regions of high political and military tension.