Pummeling air as they crossed over open water, two B-52 bombers defiantly lumbered through China’s newly declared no-fly zone.

The late November flights sent a clear message. The United States did not approve of the air restrictions China had placed over a small string of disputed islands in the South China Sea.

For more than 60 years, when the U.S. has wanted to make a military statement, it often sends in one of the country's oldest and largest planes to make the point. With its menacing appearance, its immense size and the promise of destruction carried in its belly, the B-52 Stratofortress serves as an airborne symbol of the nation's power, and Tinker Air Force Base plays a central role in keeping the iconic bomber flying.

The base near Midwest City serves as the primary depot for the B-52 fleet, responsible for maintenance, repairs and retrofitting for the longest-serving aircraft in military history. That includes billions of dollars in upgrades and overhauls designed to extend the airplane's life span beyond 2040.

Tinker estimates the program is worth $347 million annually.

“What a bargain we got as taxpayers,” said Paul Ratke, Tinker's chief B-52 engineer. “It's a big piece of giving us security, and we don't see it ending anytime soon. The reliability and robustness of this plane is enduring.”

From its origins in the Cold War to its service in Iraq and Afghanistan, the eight-engine, swept-wing behemoth has served as the backbone of the U.S. manned strategic-bomber force.

First built to carry nuclear bombs targeting the Soviet Union, today the B-52 is capable of dropping or launching the widest array of weapons in the U.S. inventory, everything from cluster bombs to cruise missiles. Many of those modifications took place at Tinker.

“Sometimes I take a minute to think about where it's been and what it's seen, and I get chills,” said Brian Waldrip, 50, of Oklahoma City, one of the 750 civilian employees who works on B-52s at Tinker.

A U.S. Air Force Boeing B-52H Stratofortress at Barksdale Air Force Base, La. U.S. Air Force

Built by Boeing, the first B-52s took to the air in 1952 and became operational with the Air Force in 1955 when the threat of nuclear war pressed at the fears of every American.

The B-52 was called on as a guardian.

During the early days of the Cold War, 12 B-52s were constantly airborne with a full payload of nuclear weapons as part of Operation Chrome Dome. With its nearly 50,000-gallon fuel capacity and midflight refueling capability, crews flew 24-hour missions. Each flight path resulted in a B-52 never being more than two-hours flying time from an enemy target, waiting for the “go codes” that would alert them to drop their devastating weapons.

“There is a famous painting of B-52s encircling the globe,” said Daniel Haulman, an Air Force historian based at Maxwell Air Force Base in Alabama. “It symbolizes the ability of the United States and the power it had all around the world thanks to the B-52.”

Boeing workers built 744 of the aircraft before the last rolled off a Wichita, Kan., production line in 1962, just as America’s involvement in Southeast Asia was escalating. It was in Vietnam that the role of the B-52 expanded from that of a strategic, high-altitude bomber, designed to eliminate an enemy’s capability and will to fight, to a tactical weapon used to support ground operations.

Retired Lt. Col. Edward Petersen, 69, of Lawton, remembers the first time he laid eyes on the giant plane that would occupy the better part of his 22-year active-duty career. He was an 18-year-old cadet at the U.S. Air Force Academy in Colorado Springs when one of the massive jets soared overhead during his induction ceremony.

While many of his classmates wanted to fly fighters, Peterson said once he got used to the size of the B-52, he enjoyed it.

“Even though it felt like you were driving a truck,” he said.

Toward the end of the Vietnam War, Petersen flew in Linebacker II, a massive, 11-day bombing campaign aimed at destroying major targets in the North Vietnamese capital of Hanoi and the seaport city of Haiphong. The so-called “Christmas bombings,” the largest since World War II, were aimed at hastening the war’s end.

B-52s flew 741 missions and dropped more than 15,000 tons of bombs during the campaign. Petersen participated in six of those runs, the most of any crew, he said. The evasive maneuvers he employed to avoid being shot down by surface-to-air missiles tested the limits of the plane.

“We were making 45-degree bank turns at 35,000 feet,” Petersen said. “You could see these telephone pole-sized missiles coming up at you, but you had to keep your course because everyone else in your formation depended on you.”

Missiles downed 15 of the planes.

In Peterson’s home office sit the throttle controls from one of the B-52s he flew during Linebacker II. He paid $500 for the controls when the plane was decommissioned and scrapped. He finds it remarkable to see the planes still flying.

During an Altus air show a few years ago, Petersen boarded a retrofitted B-52 to see what had changed.

“The major that was in charge of the plane wasn’t even born when I was a captain of one,” he said. “The body of the plane and a lot of the compartments still looked familiar, but all the tech and the cockpit looked dramatically different.”

Boeing engineer Travis Whitmer climbs in the fuel cell of a B-52 as equipment specialist Buddy MacMillan observes the procedure at Tinker Air Force Base. Steve Gooch / The Oklahoman

Today, only 76 B-52s still fly. All were built between 1960 and 1962 and over the years have undergone more than 30 major modifications to avionics, communications, engines and armament at Tinker. Recently, the base began work on contracts worth tens of millions of dollars that will allow the bomber to carry some of the newest precision-guided weapons in its bomb bay and add digital display screens, computer network servers and real-time communication uplinks to allow the crews to change mission plans, re-target weapons in flight and interact better with ground forces and other aircraft.

“It’s like taking your grandmother’s old rotary phone and giving her the latest, greatest smartphone,” said Col. John Johnson, chief of the Air Force Global Strike Command’s bomber requirements division.

Waldrip, the civilian employee who oversees wing maintenance on the B-52, is part of a family legacy at Tinker. His father, uncle and aunt all worked on planes at the base. After 28 years working on the aircraft, Waldrip said he’s stripped down so many B-52s that all that’s left of the original plane is its shape. Still, he’s become quite attached to working on the hulking giants.

“You get a lot of nostalgia from this plane because you know the history and what it has meant to our country,” Waldrip said. “I get a lot of pride knowing that I’ve done my part to help the men and women serving our country.

"I may just be putting down sheet metal on a wing, but I take pride in it.”

So does Ratke, the chief engineer, who credits the work done by Oklahomans at Tinker for allowing the unique and versatile plane’s legacy to live on.

Inside a brightly lit hangar, the deafening sound of drills and other tools fills the air. Hundreds of maintenance workers scurry over three planes spread out in the cavernous space. The gray-painted bombers sit on steel platforms that allow workers to access the planes’ underbellies. Those on top of the aircraft wear safety cables attached to their backs to save them in case of a slip that would send them falling about 35 feet to a spotless concrete floor.

As Ratke weaves his way through the maze of tool carts, spare engine parts and rigging supporting the planes, he stops beneath the bomb bay of one to explain just how many people have contributed to the legendary bomber’s continued existence.

“So many people have flown it or maintained it or worked on them,” he said. “They have all somehow touched it.”

It’s the kind of labor that’s spared the B-52 from a much different fate, said Ratke, 48, of Oklahoma City.

“That plane could’ve died 30 years ago,” he said.