John McCain was the military’s biggest booster — and one of its fiercest critics.

During his three-decade run in the U.S. Senate, McCain would often urge his colleagues to approve eye-popping increases in defense spending one minute, then admonish the military brass and their civilian bosses for wasting taxpayers’ dollars the next.

The Arizona Republican, who died Saturday after a battle with brain cancer, served four years in the House and 31 in the Senate, where he always had a seat on the Armed Services Committee. The former Navy aviator and ex-prisoner of war in Vietnam chaired the committee during his final three years as a senator, the pinnacle of his congressional career following two unsuccessful bids for the presidency.

The self-styled “maverick,” known for his hawkish foreign policy views and blunt talk, wielded an outsize influence in national security debates — advocating a muscular military, urging more defense spending and spotlighting big-ticket weapons programs that he argued squandered taxpayer money.

He famously bashed ambitious programs across the military services that overspent and underdelivered — such as the Army’s Future Combat Systems, the Air Force’s F-22 fighter and the Navy’s Littoral Combat Ship. Over the years, McCain slammed not just the Pentagon and defense contractors, but also his fellow lawmakers, for perpetuating wasteful programs.

“Over time, we have been left with a defense procurement system that has actually incentivized over-promising and underperformance,” McCain said in a 2011 speech. “In the face of the military-industrial-congressional complex, the taxpayer and the warfighter have not stood a chance.”

Sen. Lindsey Graham, an ally and one of McCain’s closest friends, called him “a reformer and a hawk.”

“We want to have overwhelming capability to deter war and win it when you get in it,” the South Carolina Republican said. “But at the same time, the military industrial complex needs watching.”

One of the few prominent U.S. lawmakers on the world stage, McCain often traveled abroad to meet with world leaders, who lately saw him as a reassuring voice during an era when President Donald Trump openly questioned the U.S. commitment to some longtime allies and institutions. He was also well known for his frequent visits to troops in war zones, including Iraq, Afghanistan and Syria.

McCain advocated significantly larger defense budgets as well as the use of military power around the world, particularly in the Middle East. And as Armed Services chairman, he slammed both the Obama and Trump administrations for failing to request sufficient funding for the military — and he railed against strict caps on defense spending set by the 2011 Budget Control Act, though he initially voted for the legislation.

After winning the Armed Services gavel in 2015, McCain used the annual National Defense Authorization Act — one of the few major policy bills to reliably pass Congress each year — to halt proposals to shrink the size of the military. With little opposition from other senators, he used the annual policy legislation to overhaul the Pentagon’s arcane acquisition system and restructure the Defense Department’s entrenched weapons-buying bureaucracy.

“The bills that he’s done as chairman are several of the most consequential we’ve had in the last 30 years,” said Arnold Punaro, who was the panel’s staff director under former Sen. Sam Nunn (D-Ga.). “The changes that he’s pushed are quite consequential.”

Even as he advocated for a bigger defense budget and broader military footprint, McCain maintained a reputation as a crusader against the billions of dollars of waste and parochial programs sloshing through the defense budget — and what he labeled the “iron triangle” of “special interests, campaign finance and lobbying” that kept the federal largesse flowing.

His criticism of big-ticket items that ran over budget and behind schedule, and his willingness to publicly admonish senior Pentagon and uniform military leaders for it, won him the ire of the Pentagon brass and many in the defense industry.

Those who knew and worked with him cite his military credentials — a 23-year Navy career that included nearly six years a POW enduring torture in Vietnam — that gave him unquestioned credibility to take on the defense establishment, fellow lawmakers and the White House.

McCain was both the son and grandson of Navy admirals and, like them, attended the U.S Naval Academy at Annapolis, Md. His two youngest sons also served in the military: Jimmy McCain is a former Marine infantryman who served in Iraq, and Jack McCain is a Navy helicopter pilot who also graduated from the academy.

“He’s seen it from the very bottom to the very top,” the leading Democrat on the Senate Armed Services Committee, Jack Reed of Rhode Island, said of McCain. “He’s seen all the extraordinary things the military has done, can do, but he’s also seen the mistakes.”

Staff and Senate colleagues often point to McCain’s role in the uncovering the Boeing tanker scandal more than a decade ago that cemented his reputation as an anti-waste crusader.

The senator lambasted criticized the Air Force’s decision to lease tankers from Boeing, approved in 2003, as far too costly and unnecessary. McCain, who doubted the Air Force’s case that its existing tanker fleet needed to be replaced urgently and opposed the service’s contracting plan as wasteful, probed the issue as both an Armed Services member and as chairman of the Senate Commerce Committee.

At the time, McCain called it “the single worst exploitation and abuse of the system that I have seen in my 20 years of public service.”

The deal was eventually scuttled, as McCain and independent watchdogs dinged the Air Force procurement strategy and Boeing was revealed to have hired the Air Force’s No. 2 acquisitions chief, Darleen Druyun, while she was negotiating the contract. The scandal resulted in a $615 million fine for Boeing and the resignation of its chief executive, Phil Condit. Druyun and Boeing’s chief financial officer, Michael Sears both went to prison.

McCain’s own career wasn’t without ethical setbacks, however: As a first-term senator, he was ensnared in the Keating Five savings-and-loan scandal, in which he and four other lawmakers were accused of improperly intervening in a probe of the Lincoln Savings and Loan Association, led by prominent financier and campaign donor Charles Keating, Jr. Although largely exonerated, McCain was rapped by the Senate Ethics Committee for “poor judgment,” and the episode dogged him for years afterward.

McCain waged a years-long fight to end funding for the Navy’s Seawolf attack submarine, arguing it was unnecessary following the end of the Cold War and would eat up too much of the service’s scare shipbuilding dollars. Estimate to cost over $33 billion for the first dozen subs, the program was eventually canceled and only three of nearly 30 planned subs were built.

He was also a persistent critic of the Army’s Future Combat Systems, the service’s largest acquisition program, once billed as a transformational “system of systems,” that cost nearly $20 billion. The program was canceled in 2009, and the complex, overly ambitious initiative has since served as a textbook example of military waste and the failures of the Pentagon acquisition system.

“To say that this program was a spectacular, shameful failure would not do it justice,” McCain said in 2011.

In recent years, McCain slammed the Pentagon for cost overruns and performance issues with the F-35 Joint Strike Fighter, which costs just under $100 million a plane and ranks as the most expensive weapons system ever. He also publicly shredded Air Force officials for keeping the total cost of the service’s new long-range bomber a secret.

And he blistered the Navy for its shipbuilding troubles, laying into his former service over delays and cost overruns in the Littoral Combat Ship and the Gerald R. Ford class aircraft carrier, among other big-ticket programs.

McCain’s introduction to Capitol Hill and the politics of defense came in 1977 as a Navy liaison to the Senate, a job he held for four years. There, he rubbed elbows with titans of the Senate like Nunn, Barry Goldwater (R-Ariz.) and John Tower (R-Texas). All would go on to chair the Armed Services Committee.

So influential was his time as a Senate liaison that, rather than accept a promotion to admiral, McCain retired from the Navy as a captain and entered politics.

He was first elected to the House in 1982. After two terms, he was elected to succeed the conservative icon Goldwater in the Senate in 1986.

In his 31 years in the Senate, McCain developed an in-your-face style that has kept witnesses on edge.

In what became a common scene during Armed Services hearings, McCain often demanded that Pentagon officials name who specifically was responsible for acquisition failures, such as the cost overrun on the Ford carrier, and whether anyone was fired for it.

More often than not, witnesses in the hot seat had no answer.

“There’s no penalty for failure,” McCain complained at a December hearing.

McCain’s hallmarks included threats to withhold funding or block nominees and propose his own solutions from the Senate. Often, he publicly admonished Pentagon brass for failing to account for taxpayer dollars.

“John does it with an edge to it, which I think is good. It’s him,” said former Sen. Joe Lieberman (I-Conn.), a close McCain friend and ally. “Everybody can’t be and shouldn’t be like John, but his willingness to go at the defense budget and the defense industry with an edge has made a lot of good things happen.”

McCain’s feud with the defense contractors, whose troubled programs he often sought to curtail or kill, was no secret on Capitol Hill. Only when he became chairman in 2015 did the industry begin to funnel him major campaign contributions.

McCain rarely hesitated to call out lawmakers’ pet projects — once famously lambasting the Alabama delegation, namely Republican Sen. Richard Shelby, for winning funding for extra ships the Navy didn’t ask for and shielding United Launch Alliance, a contractor that builds rockets in the state.

And though he warned of the outsize influence of the military-industrial complex, McCain wasn’t above using his Armed Services gavel to advance military installations and weapons platforms based back home in Arizona.

McCain, for instance, called the F-35 “an incredible waste of the taxpayer’s dollar” at a 2011 hearing, but bragged during his 2016 reelection campaign that the fighter jet would be based at Luke Air Force Base in Glendale and the Marine Corps air station in Yuma.

He also touted his efforts to stop the Air Force’s planned retirement of the A-10 Warthog attack plane, based at Davis-Monthan Air Force Base in Tuscon, and to increase production of the Tomahawk missile, which is produced by Raytheon in Arizona.

“I kinda think you could make an argument that I’m doing my job,” McCain said during an October 2016 debate with his Democratic challenger, Rep. Ann Kirkpatrick.

Nonetheless, his allies say that his views were centered on national security, not parochialism, and that he always viewed the defense budget as a means rather than an end.

“He is not somebody who says let’s have a bigger defense budget because it’s a good idea to have a bigger defense budget,” said Richard Fontaine, a former McCain aide who is now president of the Center for a New American Security. “He says let’s have a bigger defense budget because that’s what’s necessary for the United States to fulfill its security responsibilities around the world.”

“He has been a persistent advocate for more defense spending, but it’s not been mindless,” Lieberman said. “It may seem inconsistent but it’s really consistent.”