Singapore's four Gulfstream 550 airborne early warning aircraft achieved full operational capability, three years after delivery of the first unit.

The AEW twin Rolls-Royce jet-engine 550 -- a derivative of Gulfstream's business jet -- replaces the four twin-turboprop high-wing Northrop Grumman E-2C Hawkeye aircraft.

The 550 represents a boost to Singapore's defense capability, Minister for Defense Ng Eng Hen said during a ceremony at Tengah Air Base.

"The 550, together with the air force's fighter squadrons and ground-based air defense units, are a powerful network that represents a quantum jump in the ability to identify potential aerial threats early and respond decisively, in peace or in war," said Ng in a Ministry of Defense statement.

The first aircraft under the estimated $1 billion deal was delivered to the air force's 111 Squadron in February 2009 and the fourth was delivered in October, the statement said.

The aircraft's 575 mph speed, 9-hour endurance and 41,000-foot operational altitude are significant improvements over the capabilities of the Hawkeye which has been used by the Singapore air force since 1987, a report in The Straits Times newspaper said.

Hawkeyes, with a 24-foot diameter rotating dome mounted above the fuselage and wings, have a speed of around 345 mph, 6-hour endurance and an operational altitude of 35,000 feet.

Also, the Hawkeye's range is up 200 nautical miles while the Gulfstream's extends this, although The Straits Times report didn't say by how much.

The G550 also has a chaff-and-flare dispensing system to divert incoming missiles away from the aircraft.

However, the Gulfstream carries a crew of eight, versus five for the Hawkeye.

The basic Grumman E-2 Hawkeye was designed and developed during the late 1950s and early 1960s for the U.S. Navy as a replacement for the Grumman E-1 Tracer, which was retired in 1977. The aircraft entered service in 1964 aboard the USS Kitty Hawk and variants remain in active service.

In December 2010, Singapore said it was considering buying up to four U.S. Navy's surplus P-3C Orion maritime patrol aircraft, Lockheed Martin said.

Singapore, which operates five Fokker 50 maritime patrol aircraft, would pick up the Navy's surplus Orions as they are phased out and replaced by the Boeing 737-based P-8A Poseidon.

Configuration of the aircraft for Singapore would likely to be similar to 12 secondhand Orions being upgraded for Taiwan, the Lockheed statement said.

Despite Lockheed shutting down its P-3C production lines in Burbank, Calif., in 1991, there continues to be demand for revamped versions of the four-engine turboprop maritime patrol aircraft. Modernizations are done at Lockheed's Greenville site in South Carolina.