The Five Power Defence Arrangements (FPDA), set up in 1971, continues to be a "critical arrangement" for Singapore, said Chief of Defence Force Perry Lim.
The trust forged between Singapore and the other FPDA member countries - Australia, Britain, Malaysia and New Zealand - has helped the Singapore Armed Forces (SAF) work better with them in counter-ISIS operations, he added.
The SAF has supported the multinational coalition against the threat posed by the Islamic State in Iraq and Syria since December 2014.
Lieutenant-General Lim was speaking to the media after the 17th FPDA Defence Chiefs' Conference (FDCC), which was held yesterday morning at The Fullerton Hotel Singapore.
The FPDA was conceived as a transitional pact to provide for the defence of Malaysia and Singapore until the then newly independent states could fend for themselves.
The arrangements do not commit the three other countries to intervene militarily if Malaysia and Singapore face the threat of external aggression, but provide for a more consultative approach.
At the media briefing, Lt-Gen Lim said that due to the many years of relations through the FPDA, when the SAF deployed personnel in Afghanistan for six years until June 2013, it had "excellent interoperability" with the Australian and New Zealand defence forces.
At yesterday's conference, the defence chiefs reaffirmed their commitment to the FPDA, and emphasised the important role it plays in enhancing regional cooperation and security.
Australia's Chief of Defence Force Mark Binskin, speaking to reporters, said the FPDA is as relevant today as it was 45 years ago.
He said: "It's a complex security scenario today, and so, how the nations work together in a defensive means is still important to us."
Britain's Vice-Chief of the Defence Staff Gordon Messenger said Britain was committed to delivering "force elements" to future FPDA exercise programmes.
The defence chiefs also issued the FPDA Exercise Concept Directive, as they have done in previous years. It guides the development of future FPDA activities to strengthen military cooperation between the member nations.
Key exercises conducted by armed forces of FPDA countries today include Exercise Suman Warrior and Exercise Bersama Lima, both of which are held annually.