WASHINGTON - Six days before the invasion of Ukraine, Defense Secretary Lloyd Austin took a final crack at getting his Russian counterpart to admit that the Kremlin was about to launch a massive assault after assembling more than 100,000 troops at the border with its neighbor.

“I know what you’re doing,” Austin told Sergei Shoigu in an icy, deep baritone.

It was Feb. 18, and Shoigu, the Russian defense minister, had been trying to convince Austin, who was visiting Poland at the time, that the buildup of Russian forces to the north and east of Ukraine was only for routine military exercises. Austin didn’t buy it. He had seen the intelligence, and while he had yet to convince every NATO member of the inevitability of a full-scale Russian invasion, the Pentagon chief was certain of Russian President Vladimir Putin’s intentions.

The tense, last phone call between the two top defense officials - described by people familiar with how it unfolded - was among numerous actions that Austin took in the run-up to the Ukraine war, both to warn Russia and to prepare NATO for what was to come, officials said.

Austin’s blunt, forceful manner with Shoigu, and his near daily engagement with allied defense officials, stands in sharp contrast to his public image in Washington as a taciturn, sometimes silent partner on President Joe Biden’s national security team who serves in the shadow of Secretary of State Antony Blinken, national security adviser Jake Sullivan and CIA Director William J. Burns.

Austin appears content with a backstage role.

“He wants to succeed in this job,” said retired Adm. Mike Mullen, a former chairman of the Joint Chiefs of Staff who stays in touch with the Pentagon chief. “But he’s not really concerned about focusing on his legacy. It will be whatever his legacy will be, so he’s not going to burnish that up front, or try to.”

This portrait of the defense secretary is based on interviews with 15 current and former government officials, some of whom have known Austin for years. Some spoke on the condition of anonymity in order to discuss sensitive issues. Austin, through a spokesman, declined to be interviewed.

Austin has faced criticism that he didn’t argue forcefully enough to get large quantities of arms to Kyiv until Russia was already crossing the border - and that his guarded approach to public advocacy could have been a factor in Washington’s reluctance to flood Ukraine with arms before the invasion.

The response to Russia’s aggression against Ukraine has been “necessary but not sufficient,” said Rep. Mike Waltz, R-Fla., an Army veteran on the House Armed Services Committee, in an interview. “What we’re doing is certainly better than nothing - but it’s often been too little, too late.”

The Ukrainians, Waltz said, would have been better off if the United States had sent more weaponry before Russia’s invasion, rather than rapidly expanding deliveries afterward.

“Where Austin stood in that,” Waltz added, “I don’t know.”

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Austin seemed an unlikely pick for the top civilian position at the Pentagon - and not only because he was a retired four-star general assuming a role that many in Congress didn’t want to go to someone who had just been in uniform.

Retired generals were supposed to spend seven years as a civilian before they could be considered for defense secretary. Lawmakers had legislated an exception for retired Marine Gen. Jim Mattis, President Donald Trump’s choice, and prominent Democrats didn’t want to repeat the exercise. Austin, the former head of U.S. Central Command who oversaw military operations in the Middle East, had another apparent deficit: a discomfort with the public-facing parts of the job, including appearing before Congress and dealing with the news media.

Austin, however, had personal and professional connections with President Biden. The general - a devout Catholic - had attended mass with Biden’s son, Beau, when the two were stationed in Iraq. Biden, a former chairman of the Senate Foreign Relations Committee, wanted to pivot the country to a diplomacy-first model and did not want a swashbuckling secretary at the Pentagon. Austin, 68, could be trusted to provide counsel without upstaging his boss, officials said.

In the E-Ring of the Pentagon, Austin’s office projects a sense of humility and history. Few personal photographs or effects are present, despite a 40-year military career that included a Silver Star for valor earned during the 2003 U.S. assault on Baghdad. There are, however, framed homages to military pioneers, including Henry Flipper, a personal hero of Austin’s. Another Black son of southern Georgia, Flipper became the first formerly enslaved person to graduate from the defense secretary’s alma mater, the U.S. Military Academy at West Point, N.Y., just a dozen years after the Civil War’s conclusion.

“I’m honored to be the first African American secretary of defense, the 28th secretary of defense ― but I really don’t want to be the last African American secretary of defense,” Austin said at a Black History Month event in February.

Senate Armed Services Committee Chairman Jack Reed, D-R.I., said that while Austin “wasn’t someone who just walked in off the street,” he faced the same “dramatic” learning curve that all new Pentagon chiefs do.

“It’s one thing to have been in the military for more than 30 years; it’s something else to be the secretary of defense,” Reed said. “You have to answer more directly to the president, you have to answer to the Congress, you are constitutionally the civilian in charge.”

The biggest misconception about Austin is that because he is not “flashy or bombastic in public,” he is not a dynamic player in the administration, said Sullivan, the national security adviser. Austin offers Biden his unvarnished advice, Sullivan said, and does not muzzle his disagreements during weekly meetings with Sullivan and Blinken, a longtime Biden confidant, to hash out issues.

“It’s not just like everyone is agreeing with one another,” Sullivan said - though he declined to cite any specific examples of Austin swaying administration policy. “It’s an active process of going back and forth and coming up with a solution that we can all buy into.”

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Within weeks of taking office, Biden set out to follow through on a campaign promise: Ending the U.S. war in Afghanistan after 20 years. The administration deliberated on the issue for months, with senior Pentagon officials - including Austin - advising Biden that it would be wise to leave behind a force of a few thousand troops.

With Biden adamant on the issue, Austin held his tongue in public, frustrating U.S. military officials who wanted him to speak up more on behalf of the position of military leaders. Biden announced last April that he would pull all U.S. troops within a matter of months, promising an “orderly withdrawal” even as an ascendant Taliban battered Afghan forces.

The subsequent crisis consumed virtually every waking hour for Austin and his team. Armed Taliban fighters seized Kabul on Aug. 15, prompting the United States and allies to launch a chaotic and deadly evacuation from a single runway, as thousands of desperate Afghan civilians attempted to make their way past Taliban checkpoints into the airport.

Some veterans of the war called for Austin and Army Gen. Mark Milley, chairman of the Joint Chiefs of Staff, to resign. U.S. commanders later vented to military investigators that it appeared to them that Washington did not have a grasp of what was happening in Kabul.

Rep. Seth Moulton, D-Mass., a Marine Corps veteran who sits on the House Armed Services Committee, said that it was apparent to him that both Austin and Milley were “trying to do the right thing” during the Afghan withdrawal, like starting the evacuation of Afghans who supported the war effort earlier in the face of broader administration resistance.

“But at the end of the day, he is the secretary of defense - and it’s his responsibility to ensure an operation’s success,” Moulton said.

Republicans are harsher in their critiques.

“This was a moment worth pushing back as hard as possible, to the point of doing what Secretary Mattis did during the Syria context and offering to resign if the plan was executed,” said Rep. Mike Gallagher, R-Wis., a Marine Corps veteran who sits on the same panel. “If he was pushing back, clearly he was not successful in convincing the president.”

Officials said that the crisis in Afghanistan prompted Austin and his team to adopt a crisis-management mind-set during the summer of 2021, typically meeting both morning and evening on the third floor of the Pentagon to manage the exit. Weeks later, Austin brought the meetings back as the possibility of a Russian invasion emerged.

It immediately helped improve coordination, said Colin Kahl, the undersecretary of defense for policy.

“Those 17 or 18 days in August were among the most intense that I think any U.S. policymakers focused on national security have engaged in in a long time,” Kahl said. “But it generated various habits, procedures, rhythms, that have actually carried over into the Ukraine crisis in a way that, had we had to invent those processes out of whole cloth at the beginning of Ukraine, I think would have been slower.”

In addition to his regular meetings, Austin began spending early weekend mornings in the basement of the Pentagon, typically joined by his senior military assistant, Army Lt. Gen. Randy George, as he quizzed intelligence analysts about the situation in Ukraine. In October, Austin punctuated that work by making the first trip by a Biden administration Cabinet official to Ukraine, where he met with President Volodymyr Zelensky and declared that U.S. support for Ukrainian sovereignty was “unwavering.”

The trip also included stops in Georgia and Romania, and a visit to NATO headquarters in Brussels. Putin took notice, responding with a warning that Ukraine’s military development - a key component of its bid to join NATO - “really poses a threat to Russia.”

He set to work, “providing the facts, the numbers, the intelligence indicating so plainly that Russia was preparing a full-scale invasion of an independent sovereign nation in Europe,” NATO Secretary General Jens Stoltenberg said in an interview.

Stoltenberg said that Austin’s “wealth of experience” and his knowledge of what was needed “makes others listen to him when he speaks.” Another NATO official said that he speaks with gravitas punctuated with a “James Earl Jones” voice.

“He doesn’t lecture the allies,” the NATO official said, “but he knows how to put his thumb on the scale to get results.”

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A month ago, Austin found himself in Slovakia trying to broker deal to get the Ukrainians a familiar Soviet arms system - the S-300 surface-to-air missile. The Slovaks wanted a similar system in return, or assurances that the protection of one would be provided.

The Pentagon had anticipated that Slovakia would want to keep their pending agreement quiet, said Celeste Wallander, the assistant secretary of defense for international security affairs. But Jaroslav Nad, the Slovak defense minister, surprised them by disclosing the possible deal at a news conference on March 17 while standing alongside Austin. Slovakia, Nad said, was ready to turn over its S-300 “immediately” as long as its terms could be met.

Austin pressed U.S. military officials in Europe for days afterward to explain why site surveys required to send the U.S. Patriot missile system to Slovakia had not been completed, defense officials said.

“Why don’t we have an answer?” he asked during a video conference April 1. When military officials said that it would take another two or three days to complete, Austin was not satisfied.

“We need to have it tomorrow,” he said flatly.

The following Monday, the United States informed Slovakia that it would be getting a fully-manned Patriot battery deployed as soon as it wanted it. The Slovaks announced the S-300 was on its way into Ukraine, and Austin monitored its delivery, defense officials said.

“He’s not a leader who leads by fear; he’s a leader who leads by inspiration and motivation and just the quiet confidence he has in his team,” Wallander said. “He really brings the team along, and I’ve seen him be effective in that instance of Slovakia and other places.”

Sullivan said the Pentagon chief has pushed other ministers of defense “outside their comfort zones” to seal weapons transfers that have had “enormous” impact in Ukraine. Austin keeps a color-code chart tracking weapons shipments into the war zone, and keeps the president up to date with it, Sullivan added.

Gallagher, the House Republican, is unimpressed. While it’s a “welcome development” that NATO allies now appear eager to spend more on their own defense and provide weapons to Ukraine, it took “a country being invaded and pillaged in order to galvanize the West into action” under Austin’s defense strategy, Gallagher said.

Kahl, a senior adviser to Austin, rejects the criticism. For months, he said, it has been “all hands on deck, 24/7,” at the Pentagon on Ukraine.

“It’s easy for folks who are not in the system to say ‘Why aren’t you doing more? Why aren’t you going faster?’” Kahl said. “But I don’t know anybody who resides in the system who is making that argument. . . . We are literally defying the law of bureaucratic physics by how fast we are going.”