The United States Air Force is mulling the retirement of the long-running F-15C and F-15D air-to-air fighter and replacing them with upgraded F-16s by the mid-2020s. It’s a process that will no doubt be as controversial as it is complex.

The reports that service officials told lawmakers Wednesday at a House Armed Services readiness subcommittee hearing that retiring an entire class of aircraft would save costs and allow pilots to train on fewer platforms.

The service is in “deep discussions” on the matter and the F-15 inventory will be assessed further next year, Air National Guard Director Lt. Gen. L. Scott Rice. And Maj. Gen. Scott D. West, director of current operations and deputy chief of staff for operations for the service at the Pentagon, added: “The F-15C [has] served our nation well, as have its pilots for decades. And it was our air superiority fighter; now has taken that role,” according to .

The F-15E Strike Eagle wasn’t mentioned.

An outgrowth of lessons learned during the Vietnam War, the F-15 entered service in the 1970s and has been an staple across the globe ever since for the U.S. Air Force, as well as allies like Japan and Israel. The F-15C is the single-seat variant while the F-15D has two seats. It’s nothing less than iconic at this point, and probably what most people picture when they think of a modern fighter jet. It remains a formidable foe today despite its age. The U.S. still employs nearly 200 F-15Cs and F-15Ds across the globe.

One idea, Rice said, is to replace the F-15C with F-16s upgraded with AESA (Active Electronically Scanned Array) radars. The system improves an aircraft to scan for air-to-air and air-to-ground threats at the same time.

However, shelving either plane is not a done deal, according to Air Force spokeswoman Ann Stefanek.

“We’re always looking at force structure options for the future,” Stefanek said, according to Air Force Times. “Until it is something that we put in our budget as a proposal, it’s just another option that could be pursued. Just because it’s an option doesn’t mean we’ll pursue it.”

However, that the service is even considering retiring the F-15 C and D is a big deal, even if, as West and Rice said, the proposal is “predecisional.”

Here is more context on the proposal, per Air Force Times:

The Air Force is now planning for fiscal 2019, Rice said, but a decision on retiring the F-15C and D would probably not be made this year. Which means those planes would not retire until fiscal 2020 at the earliest.

But replacing the F-15 C and D—a fighter primarily focused on air-to-air operations—with the F-16, which also has air-to-surface capabilities, would raise questions. The F-15 C and D, which entered the Air Force’s inventory in 1979, carries up to eight AIM-9 Sidewinder and AIM-120 AMRAAM air-to-air missiles. The F-16, on the other hand, can carry up to six air-to-air missiles or air-to-surface munitions. Both planes carry the M-61A1 20mm multi-barrel cannon, but the F-15 can carry 940 rounds of ammunition to the F-16's 500.

Indeed, the F-16 and the F-15 are two very different planes, a point Rep. Martha McSally (R-Ariz.) made clear during the hearing. The F-16

A retired Air Force A-10 squadron commander, McSally expressed surprise at the news of the proposal before asking if the F-16 could mirror the capabilities of the F-15C, according to :

“I don’t want to get into pilot rivalries here, but if we’re talking about fourth generation assets, you’ve got the F-15C, which prior to the F-22 was the best at air-to-air … the F-16 is an incredible, versatile, multi-role, little bit less expensive sort of decathlete,” McSally said.

“Comparing the capabilities side by side …We all need to be careful through that analysis,” McSally said. “[An F-16] doesn’t bring the same capability the F-15 does with expertise in air-to-air.”

You can watch the exchange around the 1:06:36 mark below:

Rice, in response, said that the integrating all of the Air Force’s aircraft systems will make the capabilities of each aircraft less important.

Again, there is no official proposal to retire the F-15 C or D. Folks in the Air Force are talking about it—though it appears lawmakers wish they weren’t.