By Euan Graham, the Lowy Institute's International Security Program Director and Tim Huxley. IISS–Asia Executive Director

At the Pentagon on Tuesday, Singapore Minister for Defence, Ng Eng Hen, and his US counterpart, Secretary of Defense Ash Carter, issued a joint statement announcing an enhanced Defence Cooperation Agreement (DCA). This announcement (which included only scant details of the agreement itself) coincided with the 10th anniversary of the 2005 Strategic Framework Agreement on defence and security cooperation and the 25th anniversary of the 1990 Memorandum of Understanding on the US use of military facilities in Singapore.

The new DCA is, therefore, the third major iteration in the last quarter-century of a deepening US-Singapore bilateral defence relationship, one that has grown incrementally stronger ever since the late 1960s. Though not an alliance, its strategic value to the US now almost certainly outstrips that of Washington's treaty-based alliances with Thailand and the Philippines.

Singapore provides important facilities for the US Navy, including a key logistics component of US Pacific Command, and berths for visiting American aircraft carriers and submarines. The US, in turn, hosts long-term training detachments from the Republic of Singapore Air Force. Therein lies the basic reciprocity of the relationship.

The latest DCA in part reflects a natural maturing of bilateral defence relations over time. But it also indicates the value of Singapore as a crucial operating location in Southeast Asia has intensified in the context of Washington's pursuit of a larger, more evenly distributed regional military footprint. This is part of the US 'rebalance' to the Asia-Pacific, which now includes a sharper strategic focus on the South China Sea.

While much attention has lately been paid to the US Navy's freedom of navigation operations, a more strategically significant development has been a doubling, this year, of US Navy patrols in the South China Sea as a whole. Singapore's cooperation is vital to this wider effort to sustain the US Navy's regional presence, not least in terms of providing facilities for its Littoral Combat Ships (LCS).

The first operational deployment of a US Navy P-8A Poseidon maritime multi-mission aircraft to Singapore was timed to accompany this week's announcement, thus incidentally ensuring a tangible deliverable for media consumption.

The US already stages Poseidon flights out of Malaysia, the Philippines and Okinawa in Japan. However, the availability of an operating location (probably Paya Lebar Air Base) in Singapore effectively secures the 'base leg' of US maritime air patrol and anti-submarine coverage in the South China Sea. The widely-used media description of the Poseidon as a 'spy-plane' obscures its potent capability as an anti-submarine platform. This will only become more strategically significant as China's navy expands its submarine capabilities, including deployment of SSBNs (strategic missile submarines) in regional waters in the coming years. The joint statement also confirms a third LCS deployment to Singapore in 2016, as part of a plan to host up to four of the vessels before 2018.

Although Singapore is not a formal US ally (and, indeed, is believed to have turned down a US offer of Major Non-NATO Ally status a decade ago), its defence relations with Washington have become increasingly intimate, particularly over the decade since the Strategic Framework Agreement was signed in 2005. The alignment between the US Air Force (USAF) and the Republic of Singapore Air Force (RSAF), which is largely equipped with US aircraft, is especially close.

The long-term reliance of Singapore's air power on US technology was emphasised only last week, when the Pentagon (on Singapore's behalf) awarded Lockheed Martin a contract worth US$914m to upgrade the RSAF's fleet of 60 F-16s with Active Electronically Scanned Array radar systems and other major enhancements to their air-to-air and air-to-ground capabilities. It is widely assumed that Singapore will in future purchase F-35 Joint Strike Fighters, possibly opting for the short take-off and vertical-landing 'B' version of these fifth-generation combat aircraft.

RSAF units are based in the US on a long-term basis to provide training on F-15s, F-16s and helicopters, whiles USAF combat units deploy frequently to Singapore for exercises with the RSAF. Singaporean personnel are highly familiar with American operational doctrine. In short, the RSAF is equipped and trained in ways that enable it to fit into US-led operations with ease.

The public statement on the new DCA does not discuss in any depth Singapore's contribution to operations in the Middle East. Since December 2014, though, Singapore has been a military contributor to Inherent Resolve, the US-led coalition operation against ISIS in Iraq and Syria, deploying a KC-135R aerial tanker, imagery analysts and planners to support the counter-terrorist effort. At the same time, Singapore's involvement in Inherent Resolve has been typically cautious and incremental, following the pattern of its niche, mainly non-combatant contributions to US-led coalition operations in Iraq, Afghanistan and the Gulf of Aden.

Some US officials privately bemoan that Singapore may turn out to be a 'phase-zero' security partner in the Middle East context; in other words, not obliged and unwilling to move beyond providing non-combat support for coalition operations. For Singapore, which has a 16 per cent Muslim population, and is physically sandwiched between Muslim-majority Indonesia and Malaysia, to cross that threshold by contributing, for example, combat aircraft to the US-led coalition against ISIS would be difficult. The risk of domestic and local controversy may be a powerful deterrent to taking such a step.

At present, intensifying defence cooperation between Washington and Singapore is of clearer significance in the US-China strategic context. Maintaining balance in its relations with the two major powers, both of which are crucially important partners, is vital for the city-state. However, China's activities in the South China Sea have evidently disconcerted Singapore, and its support for US Navy Poseidon operations may be a signal to Beijing of its concern. In a recent speech, Prime Minister Lee Hsien Loong pointedly affirmed Singapore's determination to 'defend the rights of freedom of navigation and overflight'.

Before entering into even closer security collaboration with the US, Singapore's leaders must have weighed not only the strategic risks of following Washington down a path that in the worst case could lead to more overt confrontation with Beijing, but also the domestic political challenge of convincing a population with a 74 per cent ethnic-Chinese majority that such a course is the best one to follow. The Poseidon deployment suggests that Singapore's inclination is to help the US push back, albeit in a relatively low-profile way, against China.

Photo courtesy US Department of Defense