The partners who are helping fund the plane's development include: Britain, Australia, Canada, Turkey, Italy, Norway, Denmark and the Netherlands.
Israel and Japan have also placed orders, and Singapore may soon follow suit, according to U.S. government sources. Lockheed is also bidding for a 60-fighter order from South Korea.
Following are some key figures about the F-35 program:
COST OF THE OVERALL PROGRAM
The most recent U.S. Defense Department estimates put the current cost of developing, testing and building the F-35 multi-role fighter jet at $396 billion, a forecast that assumes U.S. purchases of 2,443 production jets, on top of 14 test planes.
Retrofits of existing planes to address problems found in flight testing are expected to total $1.7 billion over the first 10 production batches, according to the most recent report by the congressional Government Accountability Office (GAO).
The cost of operating and sustaining the new planes is estimated to reach $1.1 trillion, assuming that they will be used for 50 years, according to the most recent Pentagon data provided to Congress.
However, senior Pentagon officials have said they consider that price tag unaffordable. Program officials are taking steps to reduce the projected operating cost, including hiring enginemaker Pratt & Whitney, a unit of Hartford-based United Technologies Corp., to cut the fuel burn of the engine by 5 percent.
COST PER JET
The fifth and most recent batch of jets ordered by the Pentagon cost 4 percent less than the previous order, and prices should continue coming down steadily in the future, according to Air Force Lieutenant General Christopher Bogdan, who runs the F-35 program for the Pentagon.
The 22 Air Force models included in those contracts cost $119 million each, according to Bogdan, compared to a price of $127 million per plane a year earlier.
The cost of the three Marine Corps' B-models in the fifth order, which have a more complex engine to allow it to land like a helicopter, is estimated at $153 million per plane, down from $164 million a year ago, when the Pentagon bought 17 B-models, according to defense officials familiar with the estimates.
The seven Navy carrier variants or C-models in the fifth batch cost around $139 million, down from $148 million a year earlier, according to estimates by U.S. defense officials.
Over time, as production quantities increase, the jets are expected to start dropping in price. The per-plane forecasts factor in foreign orders, which are not included in the U.S. development, procurement and operating cost.
Current Pentagon estimates forecast that the A-model's price will eventually average out to $78.7 million per plane, while the B-model will cost $106.4 million, and the C-model will cost $87 million.
Bogdan recently said he expected to reach the target price at least for the A-model by 2020, when Australia is due to start buying the first of the 100 F-35s currently in its plans.
Lockheed executives say they believe the government's estimates are too conservative, and predict that the price of the new warplane will be even lower once the company starts full-rate production later this decade.
The most recent GAO report included a different number for the cost of the plane. It averaged the cost of all three models over the lifetime of the program, arriving at a projected average cost of $137 million per plane, nearly double the initial projected cost of $69 million.
Critics of the program say even that estimate is probably too low, noting that additional technical issues may well arise during flight testing of the new fighter jet, which is only one third complete.
Winslow Wheeler, a former congressional aide and strident critic of the F-35 program says a recent report by the Pentagon's chief tester, Michael Gilmore, raised numerous technical issues and low reliability rates that could well increase the cost of the plane in coming years.