The United States military is developing its newest jet fighter for the 21st century, a multi-role aircraft capable of combat over land and sea, offering complete air dominance.

A trio of American Armed Forces is working with aerospace engineers and nations around the world to develop the F-35 Joint Strike Fighter (JSF), the latest in advanced aerial weaponry. But instead of just one aircraft, aerospace juggernaut Lockheed Martin - which won the contract to build the fighter - has designed an airframe that supports three distinct versions of the plane to suit a variety of military uses.

"A lot of people thought that developing one plane for the Navy, Marine Corps and Air Force couldn't be done," said Lockheed spokesman John Kent in an interview. "After we finished our flight tests, though, they changed their minds."

But to replace those planes, military officials needed equipment that was both technologically superior and economical at the same time. The Navy needed a sturdy plane to take the beating of aircraft carrier landings, while the Marine Corps required vertical landing capability of the Harrier Jumpjet. The Air Force wanted a plane for air-to-ground missions that could measure up to the F-22 Raptor, also a Lockheed creation.

"To develop an individual plane for each of those purposes could cost untold billions," Kent said. But developing a standard frame that can support each use wouldn't, he added.

Capable of flying just short of twice the speed of sound, the Joint Strike Fighter is expected to cost between $37 million and $47 million per plane depending on its use. Navy versions, beefy planes with larger wingspans, lie on the higher end of the spectrum, while conventional Air Force planes will be on the lower end. Even $37 million seems much for one aircraft, but compared to its cousin the F-22 Raptor - at $100 million per plane - the Joint Strike Fighter seems to be a bargain. On top of meeting the requirements of all three military arms, the plane will be a stealth fighter as well, the first in Navy and Marine Corps history.

"The U.S.M.C. is eagerly awaiting the delivery of our first low observable aircraft," said Capt. Joseph Kloppel of the U.S. Marine Corps in an e-mail interview. The Joint Strike Fighter will also be the corps' first supersonic plane capable of a vertical landing, which provides unparalleled flexibility for military operations.

But keeping costs down may prove more difficult than Lockheed lets on.

"To some extent, we've heard this before," aerospace writer Bill Sweetman, author of the book Joint Strike Fighter: Boeing X-32 vs. Lockheed Martin X-35 and contributing editor to Jane's International Defense Review. "I think keeping the plane affordable is very challenging and that everyone is waiting to be convinced."

But Lockheed has an edge in the Raptor, a plane it began building for the Air Force in the 1990s, Sweetman said. Much of the avionics controlling the Joint Strike Fighter are descendents from Raptor control systems. The shapes are even similar, with Lockheed engineers using what they learned about stealth technology when designing the new aircraft.

"It's very much the Raptor's cousin," Sweetman said of the F-35. "So I think they have a good chance."

One of the most striking components of the Joint Strike Fighter is its ability to stop and hover in mid air for vertical landings.

The U.S. Marines Corps use the vertical-landing Harrier "jumpjets" - the British Navy's version is the Sea Harrier- to drop into locations where paved landing strips are short or unavailable. To do this, a Harrier funnels engine exhaust through vents on its belly, creating direct lift below the plane to keep it aloft. Although the method has been in use for decades, it remains dangerous. Engine exhaust spewing from a Harrier's underbelly vents can get sucked into the craft's air intake and choke the engine. Without fresh air to burn fuel, the craft loses lift and crashes to the ground.

To improve on safety and stability, Lockheed engineers fitted a lift fan just behind the cockpit. During flight, the fan is hidden behind close doors that swivel open for landing. The jet's engine turns a driveshaft - much like that on a car - that spins the fan and pushes cool air from above the plane out below. The column of cool air increases the fighter's balance as it moves downward and keeps lethal engine exhaust away from the plane's air intake.

"The bottom line is that the plane's engine puts out 25,000 pounds of thrust," Kent said. "With the lift fan, it nearly doubles that." The extra thrust isn't just for balance and show, either. The Joint Strike Fighter weighs 30,000 pounds (about 11,100 kilograms) without extra fuel or missiles, making it the heaviest plane capable of direct lift.

The Department of Defense's Joint Strike Fighter program includes a number of international partners, the most visible being the United Kingdom's Royal Navy and Air Force. But other large and small countries, including Italy, Canada, Australia, the Netherlands, Turkey, Denmark and Norway, have all had a hand in the fighter's development.

Norwegian National Deputy Rune Fagerli, the country's sole representative on the Joint Strike Fighter program, told SPACE.com the Norwegian Royal Ministry of Defence has pledged $125 million in preparations to replace a fleet of F-16 jets that have about 12 years left of operation.

"By getting involved here, on the ground level, we can try and address the needs of Norway into this capable fighter early," said Fagerli, a colonel. In Norway, for example, the runways are slippery due to wet weather and traditional F-16 jets are equipped with drag chutes to slow them down.

An international method to aircraft development could also yield aircraft that fit well together during combat, when cooperating nations are flying over hostile territory. Norwegian pilots, Fagerli cited, currently fly F-16 missions over Afghanistan alongside Danish and Dutch aviators.

Despite its uniqueness, the Joint Strike Fighter is not in a league of its own. Aerospace engineers in Europe are busy building the multi-role Eurofighter to serve as a catch-all military aircraft.

Unlike the Joint Strike Fighter, which uses one basic airframe to build three somewhat different aircraft, the Eurofighter Typhoon is a standard plane with interchangeable weapons systems that can be tailored for use over water, land and in air combat.

Lockheed and U.S. defense officials concede some competition with the Eurofighter to gain an international foothold, but feel the Joint Strike Fighter will eventually find a way to work in tandem with the opposing program.

"I wouldn't count the Eurofighter out of it yet," Sweetman said. "JSF has come on very strong and won a lot of international commitments, but there are still issues to sort out." Among them is the idea of sharing stealth technology with foreign countries, and the intended use of the plane. The Joint Strike Fighter is primarily an air-to-ground attack craft, whereas the Eurofighter functions both against ground and air targets, Sweetman added.

The United Kingdom, along with Germany, Italy and Spain, have been working on the Eurofighter since 1994, about a year after the beginning of what eventually became the Joint Strike Program. Norway has even cast a line into the Eurofighter program, deciding last month to get involved in its industrial side, while it works on the Joint Strike Fighter.

"From an operational side, we're not finished deciding what requirements we need for our new aircraft," Fagerli said. Being involved in both programs expands the number of options when the time will come to finally choose a new fighter, he added.

Although Norway doesn't have any say in the development of the Eurofighter, its involvement makes it eligible for future industrial contracts in the plane's production. The same goes for countries investing in the Joint Strike Fighter.

In the meantime, Lockheed engineers are busy refining their designs and proving the plane's capabilities. The planes should be ready for their first Air Force duty in 2008, Kent said, with subsequent models released for the Marine Corps in 2010 and 2012 for the Navy and United Kingdom. International orders will be filled after that, he added.