When Boeing's P-8A Poseidon first arrived at the Singapore Airshow two years ago, it caused a stir.
Defence buyers around the region were intrigued by the new aircraft, which was touted as reliable, capable and absolutely necessary in a region abundant with naval tension, both above and below the water.
"There is a requirement need out here in the Asian region for P-8s," Matt Carreon of Boeing said at this years airshow on Tuesday. He cited the large volume of shipping traffic, the amount of piracy and the "current political climate" as reasons why maritime patrol would be important to Asian militaries.
China has spent the past few years building up military installations around the South China Sea and its submarines are prowling farther afield, stoking Asian interest in planes that can sweep large swathes of ocean.
The number of offerings on the market has grown, too, but the cost of such specialised aircraft has kept the purchases relatively small for now.
Special-mission aircraft are a strategic asset, which goes some way to explaining why sales of such planes have remained elusive - the procurement process is very lengthy.
Among those joining Boeing in trying to address the market are Saab's Swordfish Maritime Patrol Aircraft, based on the Bombardier Global 6000 business jet; the Kawasaki P-1; the Airbus C295 MPA and proposed maritime patrol variant of its A320neo; Leonardo's ATR 72MP; and IAI's ELI-3360 Maritime Patrol Aircraft, based on the Bombardier Global 5000 business jet.
The Swordfish is not yet in production, however, and the Japanese Self-Defence Force is the sole customer for the P-1. India and Australia are so far the only Asia-region buyers of the $175 million P-8.
No big sales of maritime patrol aircraft were announced at the Singapore Airshow, which ends today (Sunday), the biggest regional aerospace and defence event.
Still, plane makers at the airshow said that Asia remained a promising market.
Two P-8s were on display at the event, one flown by the US navy - the aircraft's biggest customer by far, with 98 ordered and 64 delivered - and the other by the royal Australian air force, which has ordered 12. Britain and Norway are the only other two announced buyers.
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Gene Cunningham, Boeing's vice president of global sales for defence, space and security, said the company was in advanced discussions with South Korea over a P-8 sale. There might be a decision by the end of 2018, he added.
On Thursday, South Korea's defence procurement agency confirmed it would buy a maritime patrol aircraft from a foreign company. The Yonhap news agency, citing an unnamed military source, said the decision would be between the P-8 and Saab's Swordfish for a deal expected to be worth about $1.75 billion.
The moneymaking potential for sales in the Asia-Pacific region is clear. The US State Department gave permission last year for a nearly $1.5bn P-8 sale to New Zealand, although no deal has been announced.
Malaysia, Indonesia, Vietnam and South Korea are among others in the region shopping for maritime patrol aircraft, several plane makers said.
"If they are concerned about the proliferation of submarines, we are talking to them," said Robert Hewson, Saab's head of communications for Asia Pacific.
Mr Hewson suggested the Swordfish would be as little as half the cost of the P-8 over its lifetime.
Like Saab and others, Boeing designed its aircraft around the bones of a civilian plane, in this case the ubiquitous 737 passenger jet. Mr Carreon said the aircraft's familiarity, plus the ability add in third-party or local systems, made it attractive to even smaller customers.
"They are shocked at the value they're getting," he said.
Boeing is marketing its jet as a natural upgrade of the older, propeller-driven Lockheed P-3 Orion, which performs the same mission. Only one buyer, India, had not flown P-3s before purchasing P-8s.
Kawasaki was displaying a model of its four-engine P-1 jet, which replaced Japanese P-3s, but Hideki Yamaoka, associate officer and project manager of the company's Advanced Aircraft Export Project, said it was generally "too high-end for the requirements" of Asian customers.
Unmanned drones are another option. Joseph Song, vice president for international strategic development at General Atomics Aeronautical, which makes the MQ-9 Reaper, said he saw potential for growth in Asia.
"I think the maritime mission is going to be as big as the land mission in the future, driven by Asian customers like Australia, India, Japan, Korea, and I think Singapore and other countries will certainly play a role," he said.
After a meeting of Southeast Asian defence ministers this week, Singapore Defence Minister Ng Eng Hen said the country was spending more all around, including on ways to keep an eye on the seas around the island city-state.
"Defence spending on the whole, not only maritime surveillance, has gone up," he said. "That's a fact."