More bad news for the Pentagon's next-generation F-35 Joint Strike Fighter, the most expensive weapons program in Defense Department history – and arguably the most important one in the Pentagon today. The Air Force has confirmed what observers long expected: that the land-based F-35A model probably won't be ready for combat until 2018, two years later than previously scheduled.

The single-engine stealth fighter, built by Lockheed Martin, has been beset by parts failures, design changes and a 64-percent increase in overall cost since development began in 2001. While testing has gone better lately, the nearly $400-billion program still needs to complete thousands more test flights before the first batch of regular pilots can even begin training.

The effects of the delay are cascading throughout the world's biggest and most powerful Air Force. To keep up its strength while awaiting the F-35, the Air Force is having to keep its 1980s- and 1990s-vintage F-15s and F-16s far longer than anyone ever imagined when those planes rolled off the production line.

"We have a geriatric Air Force," retired Lt. Gen. Dave Deptula told*The Wall Street Journal *in September. And it's going to get a lot older before large numbers of new jets start offering any relief. Evolving plans see nearly 500 F-15Cs, Ds and Es remaining in the air beyond 2030, by which time the youngest C and D models – the dogfighters – will be close to 50 years old. At least 300 of the more lightly built F-16s are now expected to last through the 2020s, averaging 40 years in service. Of the Air Force's 2,000 fighters, just 180 or so F-22s can be considered "young."

With age comes increased risk of fleet-wide failures – though young planes can also have systemic problems.

Still, age is not a perfect measure of a jet's usefulness. The 50-year-old B-52 is arguably more capable than ever following decades of upgrades. The Air Force is planning billions of dollars of updates to keep the F-15s and F-16s in fighting shape. The F-15s are getting new radars and having their frayed wiring replaced. Between 300 and 600 F-16s will get structural upgrades. The Air Force is also mulling a new radar for the F-16. Both fighters could also get new weapons. "The proposed ... investments will sustain America’s air-superiority advantage," the Air Force claimed in a February statement.

Some critics disagree. With China and Russia developing new stealth fighters and America's jets still flying into their fourth and fifth decades, the Air Force could find itself outgunned in a future air war, they say. While these skeptics might take a simplistic view of aerial combat and aircraft age, they're not wrong to be alarmed at the F-35's seemingly interminable delays.

Photo: Air Force