WHITEMAN AIR FORCE BASE, Mo. (AP) — In the topsy-turvy world of U.S. strategic bombers, older and uglier sometimes beats newer and snazzier.

As the Air Force charts a bomber future in line with the Pentagon's new focus on potential war with China or Russia, the youngest and flashiest — the stealthy B-2, costing a hair-raising $2 billion each — is to be retired first. The oldest and stodgiest — the Vietnam-era B-52 — will go last. It could still be flying when it is 100 years old.

This might seem to defy logic, but the elite group of men and women who have flown the bat-winged B-2 Spirit accept the reasons for phasing it out when a next-generation bomber comes on line.

“In my mind, it actually does make sense to have the B-2 as an eventual retirement candidate,” says John Avery, who flew the B-2 for 14 years from Whiteman Air Force Base in western Missouri. He and his wife, Jennifer, were the first married couple to serve as B-2 pilots; she was the first woman to fly it in combat.

The Air Force sees it as a matter of money, numbers and strategy.

The Air Force expects to spend at least $55 billion to field an all-new, nuclear-capable bomber for the future, the B-21 Raider, at the same time the Pentagon will be spending hundreds of billions of dollars to replace all of the other major elements of the nation's nuclear weapons arsenal. The Air Force also is spending heavily on new fighters and refueling aircraft, and like the rest of the military it foresees tighter defense budgets ahead.

The B-2's viability suffers from the fact that only 21 were built, of which 20 remain. That leaves little slack in the supply chain for unique spare parts. It is thus comparatively expensive to maintain and to fly. It also is seen as increasingly vulnerable against air defenses of emerging war threats like China.

Then there is the fact that the B-52, which entered service in the mid-1950s and is known to crews as the Big Ugly Fat Fellow, keeps finding ways to stay relevant. It is equipped to drop or launch the widest array of weapons in the entire Air Force inventory. The plane is so valuable that the Air Force twice in recent years has brought a B-52 back from the grave — taking long-retired planes from a desert “boneyard” in Arizona and restoring them to active service.

Strategic bombers have a storied place in U.S. military history, from the early days of the former Strategic Air Command when the only way America and the former Soviet Union could launch nuclear weapons at each other was by air, to the B-52's carpet bombing missions in Vietnam.

Developed in secrecy in the 1980s, the B-2 was rolled out as a revolutionary weapon — the first long-range bomber built with stealth, or radar-evading, technology designed to defeat the best Soviet air defenses.

By the time the first B-2 was delivered to the Air Force in 1993, however, the Soviet Union had disintegrated and the Cold War had ended. The plane made its combat debut in the 1999 Kosovo war. It flew a limited number of combat sorties over Iraq and Afghanistan and has launched only five combat sorties since 2011, all in Libya.

The last was a 2017 strike notable for the fact that it pitted the world's most expensive and exotic bomber against a flimsy camp of Islamic State group militants.

“It has proved its worth in the fight, over time,” says Col. Jeffrey Schreiner, who has flown the B-2 for 19 years and is commander of the 509th Bomb Wing at Whiteman, which flies and maintains the full fleet.

But after two decades of fighting small wars and insurgencies, the Pentagon is shifting its main focus to what it calls “great power competition” with a rising China and a resurgent Russia, in an era of stiffer air defenses that expose B-2 vulnerabilities.

Thus the Pentagon's commitment to the bomber of the future — the B-21 Raider. The Air Force has committed to buying at least 100 of them. The plane is being developed in secrecy to be a do-it-all strategic bomber. A prototype is being built now, but the first flight is not considered likely before 2022.

Bombers are legend, but their results are sometimes regretted. A B-2 bomber scarred U.S.-China relations in 1999 when it bombed Beijing’s embassy in the Serbian capital of Belgrade, killing three people. China denounced the attack as a “barbaric act,” while the U.S. insisted it was a grievous error.

The Air Force had planned to keep its B-2s flying until 2058 but will instead retire them as the B-21 Raider arrives in this decade. Also retiring early will be the B-1B Lancer, which is the only one of the three bomber types that is no longer nuclear-capable. The Air Force proposes to eliminate 17 of its 62 Lancers in the coming year.

The B-52, however, will fly on. It is so old that it made a mark on American pop culture more than half a century ago. It lent its name to a 1960s beehive hairstyle that resembled the plane's nosecone, and the plane featured prominently in Stanley Kubrick's 1964 black comedy, “Dr. Strangelove.”

More than once, the B-52 seemed destined to go out of style.

"We’re talking about a plane that ceased production in 1962 based on a design that was formulated in the late 1940s,” says Loren Thompson, a defense analyst at the Lexington Institute, a Washington think-tank.

Rather than retire it, the Air Force is planning to equip the Boeing behemoth with new engines, new radar technology and other upgrades to keep it flying into the 2050s. It will be a “stand off” platform from which to launch cruise missiles and other weapons from beyond the reach of hostile air defenses.

In Thompson's view, the Air Force is making a simple calculation: The B-52 costs far less to operate and maintain than the newer but finickier B-2.

"They decided the B-52 was good enough,” he says.