The man often called America's top military officer, the most powerful person in uniform, actually commands nothing. No tanks, no planes, no ships, no troops.

His voice carries great weight, but he gives no combat orders.

He is chairman of the Joint Chiefs of Staff — adviser to presidents, advocate for troops, strategic thinker, and occasionally a political punching bag. He stands atop the military heap, and the role has grown in influence and public prominence, yet it remains arguably one of the least understood. In the view of some who have held the job, this disconnect has made the chairman more vulnerable to political swipes from all sides.

With the Joint Chiefs of Staff officially established after World War II, 18 men have held the job since 1949. Nine were Army generals, four were Navy admirals, four were from the Air Force and one was a Marine. (No woman is likely to fill the job anytime soon in a male-dominated military.)

Pending an expected Senate vote to confirm him this month, Gen. Joseph Dunford will be the next chairman. The commandant of the Marine Corps sailed through his confirmation hearing Thursday and is expected to take over Oct. 1 for Gen. Martin E. Dempsey, who will retire after a 41-year Army career.

The chairman is the public face of the military, but he is not in the formal chain of command linking the president to his commanders in the field. Dempsey, who is completing four years in the job, has said it reminds him of entering the Army as a lowly second lieutenant.

"I felt like I had enormous responsibility but I didn't have very much authority; that's kind of what it's like being chairman," he said in January 2014.

Today, as he looks back, Dempsey says he grew into the role, not fully realizing at the outset just how brightly the public spotlight would shine.

"In those early days that was very uncomfortable space for me. I navigated it because it is part of the job," he said.

By law, the chairman presides over the Joint Chiefs of Staff — the top officers of the Army, Navy, Air Force and Marine Corps, and since 2012, the National Guard. Collectively they form a sounding board for commanders of key combat organizations such as U.S. Central Command, and for the president and the secretary of defense. The position of Joint Chiefs vice chairman was added in 1986.

The chairman advises the president and the defense secretary on military threats, risks and options, but he bears no obligation to toe the political line of the White House. Yet this proximity to power is what sometimes makes the chairman a ready target of partisan political attacks.

Sen. John McCain, R-Ariz., for example, has accused Dempsey of being the Obama administration's lapdog.

Dempsey brushes off such criticism, calling it wrong-headed but not surprising.

"It has happened to every chairman since I've become aware that there was a thing called the chairman of the Joint Chiefs of Staff," he said in the interview. He attributes the jabs partly to a misunderstanding of the role of the chairman.

Dempsey says the chairman is supposed to be an adviser, not an advocate for any particular strategy or policy that the president may be considering. He sees his role as explaining to his civilian bosses — and to members of Congress — which military options are feasible and assessing their risks and costs. But it's up to civilian leaders to set policy goals and to decide whether to undertake any military option in pursuit of those goals.

"There's actually an acronym: pol-mil. I'm the dash," he says. "I'm the guy that lives in between the policy objectives as articulated by our elected leaders and the military activities to achieve it."

At times his advice is rejected, and Dempsey sees that as reflecting a basic feature of American democracy: civilian control of the military. In 2013, for example, he acknowledged under questioning by McCain that he had supported a proposal by then-CIA Director David Petraeus to arm rebels against the Syrian government. President Barack Obama rejected it, although last year he initiated a $500 million plan to train and equip Syrian rebels to fight Islamic State militants.

Peter Pace, the retired general who was the first Marine to hold the job, said he never shaped his advice to President George W. Bush based on politics. But politics shaped his term as chairman. Pace is seen by some as a political casualty of the war Bush started in Iraq in 2003 while Pace was the vice chairman. Bush's defense secretary, Robert Gates, announced in June 2007 that he advised Bush not to re-nominate Pace to a second two-year term as chairman because it would create a "divisive ordeal" in the Senate over the decision to invade Iraq and the mistakes that followed.

"Not being re-nominated was very much a political reality," Pace said in an interview.

In blunter language, another of Dempsey's predecessors, retired Army Gen. Henry "Hugh" Shelton, says he dodged politics like it was enemy fire.

"I did my best to isolate myself from the political arena and walk squarely down the middle — not an easy task in a city where one's party affiliation seemed more significant than his blood type," Shelton, who served as chairman from 1997 to 2001 under two administrations, wrote in his 2010 memoir.

More so than his successors, Shelton deliberately limited his public exposure, believing the national security spotlight should fall mainly on the president and defense secretary. In an interview, Shelton cited one major exception — the immediate aftermath of the Sept. 11, 2001, terrorist attacks, which left a portion of the Pentagon in smoking ruin and raised public fear about the country's vulnerability. He participated in a Pentagon news conference less than 12 hours after the attack, along with Defense Secretary Donald H. Rumsfeld and key congressional leaders.

"The American people at that point needed to see one of their uniformed (leaders)," Shelton said. "They wanted to be reassured that the military felt like they were in good shape and ready to respond."

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