After nearly 20 years of development and $65 billion, the F-22 Raptor stealth fighter entered service with the U.S. Air Force in 2005. But it wasn't until this month that the first squadron of Lockheed Martin-built F-22s was fully combat-ready with ground-mapping radars and a flexible bomb payload – standard equipment on most Air Force strike jets. The cost to bring the roughly 150 front-line Raptors up to this normal level of capability: an extra $8 billion, boosting the per-jet cost from $350 million to almost $400 million.

The belated outfitting is symptomatic of the Air Force's "spiral" approach to warplane development, and a foreboding sign for the Raptor's successor, the smaller F-35 Joint Strike Fighter. Rather than wait until a jet design is fully developed, the Air Force sends early models out into the world as soon as they meet a minimum standard for combat performance. The planes get extra enhancements over time to bring them up to full spec. While this approach ensures the flying branch gets some utility out of its new aircraft as soon as possible, it also obscures the true time and investment needed to fully develop a new warplane.

The F-22 entered service seven years ago with its air-to-air weapons mostly in place, but with only rudimentary bombing systems. Likewise, the roughly $200-million F-35 will possess only a fraction of its expected capabilities when it finally enters service sometime after 2018. That could force the Air Force to hold onto older fighters far longer than it ever expected, in order to buy time for the new jet's spiral upgrades.

This month's "Increment 3.1" update to the F-22 adds a mapping function to the jet's radar plus more accurate targeting and the ability to carry eight satellite-guided bombs. "A four-ship of Increment 3.1 aircraft can successfully find, fix, track, target and engage targets in the most challenging of anti-access environments," Lt. Col. Paul Moga told Flight. What he didn't say is that the Boeing-made F-15E has had similar skills since the 1990s.

Nor is Increment 3.1 the last planned Raptor upgrade. The F-22 isn't scheduled to get a multi-function data-link (allowing it to swap information with ground stations, ships and other planes) until around 2014. F-15s and F-16s have had these data-links for years. Similarly, the F-22 still can't fire the latest AIM-9X air-to-air missile, which is standard on older fighters. Though the F-22 possesses higher speed and better stealth than F-15s and F-16s, in other aspects it could be years before the Raptor can match the jets it's supposed to replace.