Singapore is in the “final stages of evaluating” the F-35 to upgrade its air force, a process U.S. sources say should turn quickly into orders for several dozen of the stealthy warplanes that have been beset by cost overruns and delivery delays.

Singapore, a major business and shipping hub with the best-equipped military in Southeast Asia, is expected to submit a “letter of request” soon for the F-35 Joint Strike Fighter, said two U.S. government officials who were not authorized to speak publicly on the matter.

The city-state could start the process as soon as this week to buy the planes built by Lockheed Martin Corp, one of the officials said. Pratt & Whitney, a unit of United Technologies Corp, makes the engine for the F-35.

Singapore’s defence minister, Ng Eng Hen, said on Tuesday the air force “has identified the F-35 as a suitable aircraft to further modernise our fighter fleet”.

“Our F-5s are nearing the end of their operational life and our F-16s are at their mid-way mark,” he said in parliament. “We are now in the final stages of evaluating the F-35.”

Ng gave no timeline but said the defence ministry “will have to be satisfied that this state-of-the-art multi-role fighter meets our long-term needs, is on track to be operationally capable and, most importantly, is a cost-effective platform.”

Singapore’s air force now has 24 F-15SGs, 20 F-16Cs and 40 F-16Ds, 28 F-5Ss and nine F-5Ts, according to the International Institute for Strategic Studies. It also has 19 AH-64D Apache attack helicopters among its other assorted aircraft.

The wealthy island nation of about 5.3 million people plans to spend S$12.3 billion ($9.85 billion) on defence in the 2013 fiscal year that starts in April, a rise of 4.3 percent from the previous year, the government’s budget shows.

Singapore - home to a global financial centre, the world’s second-busiest container port and major energy operations - is the region’s biggest military spender, dwarfing its much larger neighbours Thailand, Indonesia, Malaysia and Vietnam.