Robert Wall/London

For all the talk about fifth-generation-this and stealth-that, for most countries signing up to become F-35 partners there is a more basic calculation at play: The industrial return warrants the financial outlays.

Norway has now taken a big step toward potentially making the bargain work. After prolonged lobbying and badgering, Oslo secured a firm U.S. commitments to have Kongsberg's Joint Strike Missile (JSM) integrated early on the F-35.

The commitment—made in a letter from U.S. Defense Secretary Leon Panetta to his Norwegian counterpart, Espen Barth Eide—promises that JSM integration will take place. “The decision to move forward was reached following an extended dialogue with the U.S. Department of Defense aimed at securing opportunities for Norwegian industry,” the Norwegian defense ministry says in announcing the move to buy the initial two aircraft.

Several other F-35 Joint Strike Fighter (JSF) partners have shown interest in the weapon, which is still in development, with even the U.S. Navy viewed as a potential customer. Norway sees a potential of $3.3 billion to $4.2 billion in sales for the missile.

The F-35A commitment is for the first two out of a total of 52 to be bought by Norway over the duration of the program. (Oslo was going to buy 56 aircraft, but cut the number in March and stretched its production profile.) Norway estimates it will spend around $10 billion on the F-35.

The missile, to be carried inside the F-35's weapons bay, is to be integrated on JSF starting with the Block 4 configuration standard. Missile development is expected to be completed before then. Critical design review for the weapon is planned for mid-2013, with the final development phase to begin soon after, says Paal Bratlie, executive vice president at Kongsberg Defense Systems. Pre-integration studies on the fighter go back as far as 2008, with development to wrap up around 2018 or 2019, according to a Norwegian defense ministry official.

JSF flight trials are set to begin in early 2014. The JSM is derived from the in-service Naval Strike Missile, although the air-launched version uses a dual-intake and dispenses with the booster motor. Kongsberg also plans to retrofit the seeker being developed for JSM on NSM, which uses INS/GPS guidance. JSM will have land-attack and anti-ship capabilities and is being designed to have a range exceeding 150 nm even when fired at low attitude. The missile will deliver a 120-kg (265-lb.) warhead.