Hegseth is shaking up the Pentagon as the US wages war - but at what cost?

The United States military is at the centre of a fight on two fronts.

First is President Donald Trump's attempt to prise the Strait of Hormuz from Iran's grip; the latest phase of his stalemated war in the Gulf which is drawing in US forces and equipment from around the globe.

The second is a culture war at home in which Defence Secretary Pete Hegseth is conducting a promised shake-up at the Pentagon, sparking bitter recriminations and a string of departures including the top civilian in charge of the US Army last week.

The upheaval has triggered questions that could shape the legacy of Trump's second term. Is the US military being stretched to a point that could risk global security? And are these shifts leaving America's extraordinary global network of alliances vulnerable?

Last Monday there was dramatic news from the Pentagon.

One of its most senior political leaders, Dan Driscoll, stepped down as US Secretary of the Army.

Driscoll is not exactly a household name in America, let alone outside it. But his departure mattered. It was the latest twist in a power struggle within the fortress-like walls of the Pentagon over the future of the world's most formidable fighting force.

Driscoll had clashed repeatedly with Hegseth over the nature and speed of military reform. His departure was the latest in a long line of top leaders removed or sidelined by Hegseth.

The level of concern became clear as one Republican Senator Thom Tillis - a frequent Trump critic - called for Hegseth to be fired. "I have never witnessed more inept management of the brave men and women who serve our country," he said.

"This is not good news. You know, for our nation, for the army," H.R. McMaster, who served as Trump's National Security Adviser during his first term, told CBS when asked about Driscoll's departure. "Secretary Driscoll was pushing… a modernisation agenda to catch the army up."

The backstory of Driscoll's resignation cut deep into issues about the readiness of the US Army. Driscoll wanted urgent modernisation by adding drones throughout ordinary army formations to make it adept for 21st Century warfare.

He said the Ukraine war had shown how the battlefield had changed, with cheap drones and anti-missile systems challenging the US military with its vast bureaucracy and expensive procurement processes.

Hegseth had in fact initiated much of this modernisation plan but subsequently came into conflict with Driscoll, according to reports, as well as with others advocating its rapid expansion.

A source familiar with last week's departure said Driscoll had raised concerns within the administration about army readiness and transformation, which Driscoll said Hegseth was "blocking" specifically by firing the generals responsible.

Jon Duffy, a retired Navy captain and former White House defence policy official, said Driscoll's resignation showed how far Hegseth had "hollowed out" the military leadership at a critical moment.

"You lose the [army] secretary, the chief of staff and other senior leaders driving modernisation, it creates a lot of uncertainty and it disrupts momentum," he said.

"That uncertainty at leadership levels has downstream effects on the force," added Duffy, who had a 30-year career and commanded US warships before joining the White House during the second Obama administration.

In public, Hegseth - a former Army National Guardsman and Fox News pundit - has spent much of his time calling for cultural change to the US military.

He has vowed to end what he called "woke" initiatives and scrap "stupid" rules of engagement he said constrained war fighters' "lethality". He tore up diversity programmes, banned beards and railed against seeing "fat generals in the halls of the Pentagon".

He removed or sidelined the top uniformed officers in charge of the Army, Navy and Air Force as well as at least two dozen generals, admirals and civilian defence leaders, including some of the US military's most decorated officers, often with little explanation.

One critic compares the changes in the top ranks to President Xi Jinping's political purges of the Chinese military which are said to have left serious deficiencies in command structure and readiness.

"We've been conducting a military purge as well, and that has real effects on the ability of our military to be able to discharge its responsibilities," Michael Schiffer, a former top Pentagon official who covered East Asia from 2009 to 2012 under the Obama presidency, told the BBC.

"The way in which [Hegseth is] shaking them up… is bringing on board an awful lot of risk without any apparent way to be able to address or ameliorate it," said Schiffer, who is now a senior fellow at the liberal think-tank the Center for American Progress.

Asked last week about Driscoll's departure, Vice-President JD Vance defended Hegseth, saying he was in "strident agreement" about the need for a culture shift after what he called 40 years of lost wars and "military misadventures".

"What Pete came in wanting to do was revive the warrior spirit in the United States of America," Vance said.

In a statement, the White House told the BBC that President Trump had "full confidence in Secretary Hegseth and the entire Department of War whose record of success in Operation Epic Fury, Operation Absolute Resolve, and Operation Midnight Hammer speaks for itself".

Trump has continued to back Hegseth, standing by him during controversies such as Signalgate and describing him in a phone interview with NBC News last month as "actually one of my best".

Ezra Cohen, a former Under Secretary of Defence during the first Trump administration, described Hegseth's reforms as "bringing in fresh thinking and a more forward-leaning attitude".

But the reported friction among the military leadership and the stalemate with Iran has raised questions about the future of the US military at a critical moment.

Trump's order to launch strikes on Iran on 28 February led to a significant global redistribution of US military resources over the subsequent months. US weapons stored in Europe and Asia were transferred from those regions to replenish supplies in the Gulf.

Europe is now feeling significant "blowback", according to Professor Liana Fix, a Germany-based expert at the Council on Foreign Relations.

She said the lack of communication by the Trump administration with its Nato and European allies ahead of the attack on Iran left relations reeling and accelerated a strategic decision already in process to shift some US military resources away from Europe, particularly as Trump complained that his European allies weren't helping.

Prof Fix said in that context Russian President Vladimir Putin had escalated so-called "hybrid" attacks involving armed drones or sabotage attacks on Nato countries like Germany. Russia denies carrying out the attacks.

"What [Putin] is seeing is not a united stance from the United States and the Europeans to further increase pressure on Russia… he sees that they are weakening, that there are windows and openings of vulnerabilities in Europe," she told the BBC.

Last month, CIA Director John Ratcliffe paid a highly unusual visit to Moscow. He is reported to have delivered a warning to the Kremlin not to test Nato's resolve. But at the same time, one of Hegseth's top officials at the Pentagon, Elbridge Colby, was in Europe to push countries to spend more on their own defence.

Washington had announced a cut of 5,000 from a total 40,000 US troops based in Germany, while a Biden-era plan to deploy a US battalion with long-range Tomahawk missiles to the country was being dropped.

The drawdowns in Europe fit the Trump administration's strategy that predates the Iran war. It sees the Pacific region and Washington's rivalry with China as America's number one national security challenge.

But while the fallout from the Iran war has exacerbated Trump's irritation with Europe and accelerated some US military moves away from the region, it has not been to the immediate benefit of the US presence in the Pacific.

In fact, Washington has also pulled resources from there. Carrier forces were diverted from the Pacific to the Gulf, including the USS Abraham Lincoln and later the Japan-based USS George Washington.

The war is widely assessed to have left critical stocks of American ammunition badly depleted. The US fired about a third of its 3,000-strong stockpile of Tomahawk attack missiles, according to the Washington DC-based Center for Strategic and International Studies (CSIS).

Its air defence munitions were burned up at an even higher rate, with nearly 1,500 Patriot interceptors - used to shoot down aircraft and cruise and ballistic missiles - fired out of a stockpile of around 2,300, according to the CSIS.

White House Principle Deputy Press Secretary Anna Kelly said America's "military might" was "stronger than it's ever been".

"The United States Military has more than enough munitions, ammo, and stockpiles to serve all of the Commander-in-Chief's strategic goals and beyond," she said.

Meanwhile Ezra Cohen, the former Trump defence official who is now a fellow at the Hudson Institute, described the president as having degraded Iran's conventional military threat.

Iran's proxy groups are weaker than ever, he said, and in many places they have been completely obliterated, meaning "the president now has additional options and forces in the region to strike other Iranian targets, including nuclear targets, at will".

The strikes might yet take place again. Thousands of troops, including the 82nd Airborne Division, were sent to the Middle East more than six months ago for a deployment that is now stretching into 2027 with no obvious end in sight.

Pictures last week of the USS Abraham Lincoln docking in Thailand with a rusting hull after a gruelling nine months at sea in the Gulf were pounced on by Iran. The regime tried to portray it as a symbol of America's spent efforts.

Hegseth, meanwhile, forcefully rejected claims of abysmal conditions on board. But the narrative war reflected the challenge for Trump and Hegseth as they fight to transform the Pentagon while waging a costly, protracted war.