WASHINGTON - The United States government has given the green light for the sale of up to a dozen elite stealth fighter jets and related equipment to Singapore for US$2.75 billion (S$3.7 billion), it said on Thursday (Jan 9).

Singapore first announced its plans to buy the F-35 jets from Lockheed Martin Corp to replace its ageing F-16 fleet, which has been in service since 1998, in March last year.

Singapore's purchase of the F-35B jets, a pricier variant that can take off from shorter runways and land vertically, must still be approved by the US Congress, but is expected to pass. Congress was formally notified of the proposed sale on Thursday and will have 30 days to review it before it is approved.

"Singapore is a strategic friend and major security cooperation partner and an important force for political stability and economic progress in the Asia-Pacific region," said the Defence Department in a statement.

It said that the proposed sale of F-35s would augment Singapore's operational aircraft inventory and enhance its air-to-air and air-to-ground self-defence capability.

The F-35s would add to Singapore's effective deterrence to defend its borders and contribute to coalition operations with other allied and partner forces, added the Defence Department.

It said that Singapore requested to buy four F-35Bs with the option to buy eight more of the same aircraft, as well as up to 13 engines, electronic warfare systems and related support and logistics services.

In a statement on Friday, Singapore's Ministry of Defence (Mindef) said it submitted the request to the US on April 5 last year.

Mindef said the Congressional Notification (CN) of Singapore’s request adheres to the formal requirement within the US for possible sale of military equipment to foreign countries.

"It is routine and Congress has 30 days to respond to the CN," the ministry said in the statement, adding that "the CN is not a formal contract of purchase".

"If the CN passes, formal terms will be negotiated for the Letter of Offer and Acceptance," said Mindef.

Singapore would be the fourth country in the Asia-Pacific region to own F-35 jets, after Australia, Japan and South Korea, said S. Rajaratnam School of International Studies airpower analyst Ben Ho.

Said Mr Ho: "The acquisition of America's most advanced warplane would mark a quantum leap in capability for the RSAF fighter force and the SAF as a whole. The F-15s and F-16s currently in RSAF service are considered 'fourth-generation' aircraft, while the F-35 is a fifth-generation one.”

The F-35’s advanced sensor array allows it to send target information to friendly aircraft and surface forces, for instance relaying information to non-stealthy F-15 jets without the latter activating its sensors and compromising itself, he said.

The jets can also be deployed from less-than-ideal operating conditions, for instance from a long stretch of road, should regular airfields be rendered inoperable from enemy action, he added.

The F-35B jets cost US$115 million a unit, compared to the F-35A model, which has conventional take-off and landing capabilities and a US$90 million price tag, according to figures cited by Defence Minister Ng Eng Hen during Mindef's budget debate in March last year.

Dr Ng noted that the price of the F-35 jets had been falling steadily over the past decade due to healthy orders. The price of each unit has since come down even further.

Defence technology analyst Kelvin Wong of military publication Jane's said that the more costly F-35B model would sacrifice range and internal payload capacity compared with the conventional F-35A, for the ability to do short take-offs and vertical landings.

It can operate from facilities with little infrastructure and take-off fully loaded in distances as short as 167m.

He noted that the F-35B would be the Republic of Singapore Air Force's first aircraft with fixed wings that has the ability to do short take-offs and vertical landings.

But the projected closure of Paya Lebar Air Base from about 2030 to make way for commercial and residential developments would make the F-35B an ideal aircraft to enable the RSAF to continue mounting air operations from alternative facilities like Sembawang Air Base and temporary highway airstrips if needed, he said.

It was also a good idea for Singapore to acquire four F-35Bs first and evaluate their performance in Singapore's hot and humid tropical climate before committing to a larger buy, he said.

This would allow the authorities to see if the aircraft was able to withstand constant exposure to airborne salinity and impurities in those operating conditions, and enable them to develop more cost-effective preventive maintenance and repairs, he added.

With additional reporting by Lim Min Zhang