If you’re the Pentagon, how do you choose between an aging, but dependable, fighter jet and a brand new aircraft that you’re not quite sure is up to the job? You have them fight it out, naturally.

That’s essentially what the Air Force said it would do when it announced that starting in 2018, it would pit the A-10 “Warthog” against the F-35 Joint Strike Fighter in a series of tests to see if the new F-35s can adequately replace the A-10s, which the military wants to retire. A 40-year-old platform, the A-10 has been described by Martin Dempsey, the joint chiefs chairman, as “the ugliest, most beautiful aircraft on the planet.” It may be old, but as a certain Irish actor would say, it has a very particular set of skills: The A-10 excels at providing what’s known as “close-air support,” flying low and slow to provide ideal cover protection for U.S. troops fighting in ground combat. That capability is prized not only by the military, but also by a pair of key Republican lawmakers who oversee its budget, Senators John McCain and Kelly Ayotte.

The $400 billion F-35 program has been maligned for its production delays and unprecedented expense, and while the snazzy (and stealthy) new joint strike fighters are expected to be able to do many things well once they’re fully ready around 2021, there’s concern that they won’t be able to match the A-10’s close-air support capability. McCain, who heads the Senate Armed Services Committee, and Ayotte have been campaigning to get the Defense Department to drop its plans to retire the A-10 by 2019 to save money, in large part because of those worries. As a result, the Pentagon is setting up a “comparison evaluation” to see if the F-35 can measure up. “You can’t guess at what the capability gaps are,” J. Michael Gilmore, head of the Pentagon’s testing operation, told reporters at the Pentagon. “It’s really not wise to guess. You have to go out and get data and do a thorough and rigorous evaluation.”