A Canadian female infantry officer commanded the troops guarding the Queen and royal residences in London on Monday.

Capt. Megan Couto, 24, led some 40 Canadian soldiers through the changing of the guard at Buckingham Palace. The 35-piece Royal Canadian Artillery Band led the way, performing and marching along The Mall under the blazing sun as a crowd of a few hundreds tourists watched from the sidewalk.

The band performed Leonard Cohen's Hallelujah and the theme song to Hockey Night in Canada.

The Canadians could be distinguished from the usual British foot guards by their grey headwear, called pith helmets, rather than the black bearskin helmets worn by British guards.

Next, Couto settles in as the captain of the guard, based at nearby St. James's Palace, for 24 hours of duty.

"It is just another day on the job," said a calm Couto. "But it is a pretty special one for me."

Watch as Canadian Soldier Captain Megan Couto becomes the first female ever to Captain The Queen's Guard during Changing the Guard. <a href="https://t.co/iSjgX98Eaz">pic.twitter.com/iSjgX98Eaz</a> —@RoyalFamily

Canadian troops on patrol

Canadian soldiers are serving as the Queen's Guard on select dates until July 3, keeping watch as sentries at Buckingham Palace, St. James's Palace, the Tower of London and Windsor Castle. The Queen had invited Canada to send troops to assume the ceremonial duties in 2017 — a way of marking 150 years since Confederation.

"It's pretty surreal," said Maj. Jay Hudson, the officer commanding the Canadian contingent. He has served in Afghanistan and Ukraine but said "this is the last thing you would expect to do within your military career."

Couto will become the first female infantry officer to command the Queen's Guard on Monday. 'I think anyone would be excited,' she said of the honour. (Jared Thomas/CBC)

Hudson commanded the guard for the first time last week, admitting there were "a bit of jitters." He stepped aside temporarily Monday to give Couto, his second in command, the chance to lead.

"The mood has settled a little bit and we're excited for our next mount," he said.

British troops usually assume the guard role, but units from the British Empire and Commonwealth have done so on occasion. Soldiers from the 117th (Eastern Townships) Battalion, Canadian Expeditionary Force, were the first Canadians to act as the king's guard for George V in 1916.

Making history

Women have participated , but never before has the sovereign's guard been led by a female infantry officer.

The British Armed Forces don't allow women to accede to some frontline roles due to "previous concerns" over "muscular injury, psychological health, and impaired reproductive health," said Susan Coulthard, a spokesperson for the British Ministry of Defence. Infantry roles will be accessible to female troops by the end of 2018, she added.

Canada's military has allowed women to serve in nearly all roles since 1989. (The exception was submarine service, though that ban was lifted in 2000.)

Buckingham Palace, the Queen's central London residence, attracts crowds of tourists every day of the year. (Thomas Daigle/CBC)

"A lot of the things that I do, I am the first," said Couto, a graduate of the Royal Military College of Canada. "But that's kind of the blessing that in Canada, it's not that huge of a deal."

The Toronto native joined the Armed Forces in 2010. A member of the 2nd Battalion, Princess Patricia's Canadian Light Infantry, based at CFB Shilo, Man., she was previously deployed to help Saskatchewan battle forest fires in 2015.

Flashing a smile but disguising any overt excitement, Couto admits she only recently learned that Canadian soldiers sometimes guard the Queen.

"It is a big deal because of the tradition and the importance of the ceremony," Couto acknowledged, while downplaying the significance of her own achievement as a woman.

"We brought all of our normal people and I'm one of those people, just doing my job."

Security on British minds

Changing of the guard ceremonies were briefly cancelled in May following the deadly bombing in Manchester. Prime Minister Theresa May ordered troops be deployed to key sites, including Buckingham Palace, in the days following the attack.

Despite the recent violence at Westminster Bridge, London Bridge and Finsbury Park, the Canadian soldiers on patrol don't expect to be called into action.

The 24-year-old Couto joined the Armed Forces in 2010. She's based at CFB Shilo, Man. (Jared Thomas/CBC)

"Our duties are purely ceremonial," said Hudson. "We know that the police are there in the event that something were to happen."

Whatever goes on, Couto expects weeks of rehearsals will pay off on Monday.

"We'll be well prepared," she said. "It's a great opportunity for us to come out and show what Canadians can do."