The United States is Singapore's most important strategic partner. Similarly, the role Singapore plays in American strategic presence in the Asia-Pacific is unique and critical.

Within a web of defence relationships that the US possesses in the Asia-Pacific, the Singapore-US strategic partnership stands out because the depth of its commitment stops short of mutual defence treaties. Instead, Singapore's defence relations with the US focus on shared interests and avoid the entanglements of mutual defence commitments.

This week, the two countries agreed to boost defence ties through the signing of an agreement that paves the way for enhanced cooperation in a broad range of areas, including, for the first time, cyber defence and biosecurity.

The signing comes at a time of change for security in the region.

Since the end of the Cold War, domestic voices within American allies, such as New Zealand, the Philippines, Japan, South Korea and Australia, have questioned their alliance relationships with the US.

Rising nationalist movements and groups in these countries associate American bases with the loss of sovereignty, sometimes forgetting that America's strategic presence pays security dividends. As American allies face increased stress to untether from Washington, the Singapore-US defence relationship bucks the trend.

Singapore's pragmatic and business-like approach towards defence cooperation with the US not only provides a practicable alternative to the current state of American alliances in the Asia-Pacific, but is also embraced in Washington because Singapore does not ask for American protection.

Rather, Singapore takes measures to ensure its own security, which premises on deft diplomacy and credible deterrence.

Singapore adopts a foreign policy of non-alignment and engages with its partners on the principles of mutual interests. Hence, the alignment of interests between the US and Singapore in the Asia-Pacific forms the bedrock for an enduring defence relationship.

During the Vietnam War, for example, Singapore-American defence cooperation took the form of repairs and maintenance services for US military ships and aircraft, first managed by the British colonial authorities and then continued by the Singapore government after independence. Because of the high demand for these repair services, along with the refuelling of US vessels and the Rest and Recuperation Programme of American troops in Singapore, Singapore managed to avoid dire economic and security crises that could have resulted from Britain's military withdrawal from the late 1960s to early 1970s.

In fact, the withdrawal of British troops created a pressing need for a counterweight to balance Sino-Soviet influence in South-east Asia during the height of the Cold War.

The US was the only power able to play that role.

Since independence, Singapore has recognised the importance of having a balance of power in the region and, therefore, actively engages the US and rising regional powers, such as China and India.

Nations in the region find American strategic presence acceptable, particularly because the US regards the peace and stability of the Asia-Pacific to be important for its own interests.

Furthermore, scholars point to the success of American soft power in cultivating an image of a dominant and benign power in the region.

As a small nation, Singapore thrives within a stable regional environment that is dominated by a superpower like the US.

In the nascent years of building Singapore's own defence capabilities, military equipment and technology from the US catalysed the development of the Singapore Armed Forces.

The US also provided some of the overseas training space that the Singapore Armed Forces (SAF) utilised and conducted joint military exercises in.

For instance, the SAF utilises training locations in Luke and Mountain Home Air Force Bases, Silverbell Army Heliport and Grand Prairie, Texas.

Both militaries have also been conducting annual bilateral exercises since 1980.

Exercise Tiger Balm, the longest-running bilateral exercise between the Singapore and United States armies, has been running for 35 years.

This year also marks the 25th year of Exercise Commando Sling, which involves both air forces.

The Republic of Singapore Navy and the US Navy recently commemorated the 20th year of Exercise Cooperation Afloat and Readiness Training (Carat), a bilateral naval exercise held annually.

Today, Singapore-US defence cooperation has gone through significant enhancements.

The memorandum of understanding (MOU) signed in 1990 was a key agreement, which allowed wider use of Singapore's facilities by the US military.

Under the provisions of the MOU, the Commander, Logistics, Western Pacific (Comlog Westpac) of the US Pacific Fleet moved to Sembawang after the Command vacated Subic Bay and Singapore provided logistical support for transiting US forces, aircraft and vessels.

The hosting of Comlog Westpac in Sembawang demonstrates Singapore's belief that American strategic presence in South-east Asia should outlast the Cold War.

In 1998, an addendum to the MOU was signed so that US military vessels, including deep draft vessels, could stop at the new Changi Naval Base.

The Strategic Framework Agreement (SFA) signed in 2005 extended the 1990 MOU and increased the areas of defence collaboration between Washington and Singapore, especially in managing global terrorism.

The SFA enhances the bilateral and multilateral military exercises between both countries and deepens the strategic dialogue and exchanges in defence intelligence, among other areas.

The rotation of US Littoral Combat Ships through Singapore, as well as through other forward operating facilities in the Asia-Pacific, serves a critical function for the region as it demonstrates the rebalancing of the US to Asia and performs humanitarian assistance and disaster relief missions.

Regional and global security dynamics have changed since Singapore and Washington last signed the SFA.

More than a decade since 2005, more security risks have emerged in higher frequency and intensity. The growing influence of China and India will alter the Asia-Pacific balance of power in time to come.

Territorial disputes in the East China Sea and South China Sea threaten the geopolitics of the region, if allowed to escalate into conflict.

Transnational terrorism remains a security risk, and has recently taken on a cyber and informational dimension through the use of social media and retaliation by "hacktivists" after the Nov 13 Paris attacks.

The world is constantly changing. But the fundamental interest of regional security shared by both Singapore and the US remains constant, and growing their strategic relationship to help tackle emerging threats would be a sensible endeavour.

• The writer is a Research Fellow with the Military Studies Programme at the Institute of Defence and Strategic Studies, S. Rajaratnam School of International Studies (RSIS).