Hidden among hills, mostly in tunnels, hundreds of North Korean heavy artillery pieces stand ready to rain thousands of shells a minute onto Seoul. For decades, the big guns have been the biggest threat that South Korea has had to face. More recently a new one has become more prominent in the South's strategic calculations: an uncertain number of nuclear warheads of uncertain performance and reliability, potentially fitted to ballistic missiles fired from heavily protected sites in the far north of the Korean Peninsula.

No wonder, then, that strike and survivability are key requirements in South Korea's F-X Phase 3 contest for 60 fighters.

But look a bit further. Even if North Korea collapses, South Korea will remain a neighbor of authoritarian, nationalistic and increasingly assertive China, which says it will field an advanced new fighter in 2017-19. And a united Korea would also have a border with Russia, which is developing its supercruising, stealthy PAK FA fighter.

That explains why the South Korean air force ranks air-to-air capability equally with strike as it seeks parliamentary funding for the program, with the aim of choosing the Boeing F-15SE Silent Eagle, Eurofighter Typhoon or Lockheed Martin F-35 Joint Strike Fighter next year.

Pressed to nominate a priority, one program official says that an excellent strike capability would be valued more highly than an excellent air-to-air capability. Rapidly knocking out those guns, and ranging far into North Korea to hit ballistic missile launchers, nuclear facilities and command nodes would be critically important if war came.

That is one reason the stealthy F-35 is a strong contender for the order. But the repeated delays to the Joint Strike Fighter program are strengthening the hands of the F-35's competitors.

F-X Phase 3 currently requires a first delivery in 2016, with initial operational capability in 2018, says air force Col. Taek-Hwan Song, who addressed a seminar on the program in Seoul last month held by the Korea Defense and Security Forum. The target dates should be easy for Boeing and Eurofighter to meet, but maybe not for Lockheed Martin.

The issue is not so much making deliveries in 2016. Lockheed Martin says that, since the company will deliver 135 F-35s to the U.S. and its partners in 2016, a handful for South Korea should not be too much of a problem.

Rather, the difficulty lies in getting a novel aircraft type into service at almost the same time as its lead customer. While the U.S. definition of “operational” is more demanding than South Korea's, it is clear that the F-35's schedule is now tight for a customer whose old fighters will run out of life around the end of the decade. It would be very hard to keep flying the aircraft that the F-35 is to replace—F-4 Phantoms and F-5 Tigers—past 2020, says Song. Australia, a committed F-35 customer, is in much the same position (AW&ST May 16, p. 27).

F-X Phase 3 could easily slip, however, boosting the F-35's chances. The overall F-X program first emerged in 1988, and it took until 2002 before parliament had loosened its purse strings enough to allow the order of a batch of fighters under Phase 1. Parliament may not approve funding for Phase 3 this year.

A further complication is the demand that the winning bidder transfer technology to help South Korea to develop its proposed KF-X fighter. This requirement is now backed by the air force, which previously looked askance at the costly ambitions of the technologists in the defense ministry (see p. 22).

On this point Eurofighter, represented in South Korea by EADS, has a clear advantage over its U.S. competitors, since it is not subject to Washington's strict rules on technology transfer. Eurofighter proposes that the Typhoon become the basis of KF-X, diminishing risk for the ambitious but still insufficiently experienced local industry.

Still, as a non-U.S. supplier, Eurofighter must wonder whether it is being used only as a stalking horse for Boeing and Lockheed Martin. The local military's habit of buying U.S. equipment and the great effort that the U.S. puts into defending South Korea are factors that cannot be overlooked. Yet they also should not be overstated. EADS unit Eurocopter is supporting the development of South Korea's Surion utility military helicopter.

Related to the issue of technology transfer, the Typhoon can also be put into local production, an important issue for local industry, since Korea Aerospace Industries (KAI) will probably need a replacement for the production line of its FA-50 light attack aircraft, a derivative of the T-50 superlsonic trainer, this decade.

Major parts of the F-15 are already in local production, since the type won F-X Phase 1 and 2, with orders for 40 and 21 F-15Ks, respectively. Boeing's technology-transfer offer is based partly on KAI working on the Silent Eagle, which at this late stage in the F-15's development cycle introduces fly-by-wire flight controls, weapons bays and canted tail fins.

KAI builds the wings and forward fuselages of F-15s for all customers, and could step up to a larger share of the aircraft structure if the big new order went to Boeing. For the Silent Eagle, KAI is helping to develop and make conformal packs fitted to each side of the aircraft to house munitions, equipment and fuel. South Korea is not the only country interested in fitting them, says Brad Jones, director of Boeing's U.S. Air Force F-15 development programs. The packs will presumably be an option for the F-15Ks of Phase 1 and 2.

The canted fins of the Silent Eagle are not a large structural change that could threaten the 2016 delivery date, says Boeing. A new mounting structure is used but the fins themselves are unchanged from those of earlier F-15s.

While KAI has plant and trained workers for making F-15s, the air force has the equipment and skills needed to maintain them, thanks to the two previous phases of F-X. Accordingly, Boeing reckons its bid is the cheapest.

In other competitions Boeing must contend with a presumption that the customer will eventually buy the F-35 anyway, raising the temptation of moving on to that generation immediately. But South Korea's plans—if they survive the perils of budgets and development challenges—suggest that F-X Phase 3 is Lockheed Martin's only chance to sell its fighter to one of the biggest buyers of Western combat aircraft. The country's next fighter requirement after F-X—F-XX—is supposed to be filled by the indigenous KF-X. Then the combat aircraft after that is to be pilotless.

F-X Phase 3 thus offers the South Korean air force an opportunity to consolidate its top-end fighter force on 120 F-15s, eliminating an intermediate type—but only if it bets that its two follow-on domestic programs will succeed.

The F-35 enjoys an obvious advantage as South Korea ponders its strike mission, although Boeing and Eurofighter argue that there is much more to stealth than an all-aspect low radar cross section, and that there is much more to survivability than stealth. South Korea has not yet modeled the effects of characteristics such as radar cross section and flight performance. Eurofighter, apparently confident of what South Korea will discover, urges it to do so. The air force suggested in 2008 that it could not accept compromises in flight performance, an attitude that would favor the Typhoon and Silent Eagle, with their low wing and thrust loadings, not to mention outright speed.

As in Japan's similar fighter competition (also, confusingly, called F-X), Lockheed Martin will seek to satisfy South Korea's demand for technology transfer by allocating offset work that will bring know-how from outside of the F-35 program. Some F-35 manufacturing is also available for allocation.

It is quite unlikely that South Korea would be allowed to build the F-35, since manufacturing is part of stealth technology. A final assembly line, as in Italy, is possible, but would cost at least $1 billion—and bring only the techniques of final assembly, a small part of the process of building a fighter.