Army Secretary Mark Esper and Gen. Mark Milley, the service’s chief, will soon take their partnership to the highest levels of the Pentagon as both men are poised for speedy confirmation to be the next Defense secretary and Joint Chiefs of Staff chairman.

Their close working relationship could help provide stability at the Pentagon, where many of the top jobs are filled by acting heads. Meanwhile, their deep ties to the Army could give the sometimes embattled service — which has struggled for two decades to modernize its force and adapt to a new era of warfare — a place of new prominence in the Pentagon.

Esper, a West Point alum, spent 10 years on active duty, including deploying during the Gulf War with the 101st Airborne Division. Milley, a career officer, has served tours as a commander in Iraq and Afghanistan.

The probable ascension of two leaders with Army backgrounds to the top of the Pentagon’s ranks is particularly notable because the previous permanent occupants of those roles, former Defense Secretary James Mattis and outgoing chairman of the Joint Chiefs Gen. Joseph F. Dunford Jr., are both Marines.

The Senate Armed Services Committee approved the nominations of Esper and Milley last week. Esper is expected to easily clear a Monday vote to cut off debate on his nomination, with a final confirmation vote likely Tuesday. A vote on Milley’s nomination hasn’t yet been scheduled.

No favoritism

Shared experiences and similar backgrounds can help forge a strong working relationship, said former Defense Secretary Chuck Hagel. But, Hagel stressed, don’t expect them to show favoritism toward the Army.

Hagel, who served in Vietnam as an Army officer, led the Pentagon while Army Gen. Martin Dempsey was Joint Chiefs chairman.

“We were very, very close,” said Hagel, who spent 12 years as a Republican senator from Nebraska before becoming President Barack Obama’s third Defense secretary in 2013. “The fact that we were both Army veterans didn’t make any difference at all at how we saw the other services.”

The infighting between the military services was a notorious problem before the 1986 Goldwater-Nichols Department of Defense Reorganization Act, which forced the services to approach many key tasks in a joint, cooperative matter.

In the decades since, Goldwater-Nichols has achieved its goal of creating a joint force, and the services are deeply integrated, Hagel said. Officers from different branches lead the military’s combatant commands, he noted.

Hagel said he never heard anyone suggest Mattis tilted things in the Marine Corps’ favor, although the quick transition from general to Defense secretary — Mattis required a waiver to forego the seven-year waiting period required by law before a retired officer can become the Pentagon’s top civilian — meant his relationships with fellow officers were still fresh.

“I’m sure because Mattis had almost 40 years in the service with Marines, his relationships and awareness and knowledge of fellow Marine officers” like Dunford “didn’t bias him but made him more comfortable” with them, Hagel said. “That would be natural.”

Gary Roughead, a retired admiral who served as the Navy’s chief during the George W. Bush and Obama administrations and is now a fellow at the Hoover Institution, agreed that Esper and Milley’s Army backgrounds wouldn’t interfere with their responsibilities to lead the entire military.

“Some will likely allege an Army bias, but that will be wrong and unhelpful,” he said. “I have no doubt they will be impartial as they grapple with the range of security and military challenges and capability, capacity, and readiness pressures.”

Some risk

But Ray Mabus, who served as Navy secretary throughout the Obama administration, worried that their common background could create a strategic blind spot.

“The bigger risk, and it is a risk, is that you’re only going to get one point of view,” Mabus said.

Both Esper and Milley were infantry officers, which could color their approach to future conflicts, he said. Under the National Defense Strategy, the Pentagon’s touchstone planning document produced during Mattis’ tenure, possible future conflicts with China or Russia will likely rely heavily on air and sea assets, Mabus noted.

Possible hotspots like the Strait of Hormuz, the South China Sea and North Korea aren’t very likely to require the kind of heavy, armored divisions that the Army brings to bear, he said.

“The force right now was built for Iraq and Afghanistan,” said Mabus, a former Democratic Mississippi governor. “If you have two people, both of whom their first instinct is going to be heavy infantry, you don’t have the breadth of advice or the debate.”

Meanwhile, the new leaders’ familiarity with the Army may affect Pentagon planning, particularly on how to structure the force, Mabus said.

“There are not many folks who think you need a 500,000 [person] Army now, except in the Army,” he said. “That’s the danger I see. If you spend that money on infantry, you’re not spending it on things like cyber or things like more gray hulls for the Navy, or space, or the Air Force.”

And it is only natural for services to vie for as big a piece of the pie as possible.

“There’s no question that there are these inter-service rivalries, no question at all,” he said. “And for that reason, there is no question that you need objective leadership at the top.”

Mabus, who says he knows Milley well but doesn’t really know Esper, insisted he wasn’t questioning the competence or patriotism of either.

“It’s just their background,” he said. “But everybody tends to view things through the lens of their experience. And it’s just something to be aware of.”

John M. Donnelly and Patrick Kelley contributed to this report.