Boris Johnson has joined Ukrainian soldiers on a training exercise in North Yorkshire.
In a video released on his social media pages, the Prime Minister can be seen throwing a hand grenade, using a machine gun and holding a rocket launcher.
The military drills are part of UK efforts to support Ukrainian troops as the war with Russia continues.
Earlier this month the first cohort of soldiers arrived in the UK to be trained by British forces.
The Ministry of Defence announced the programme will train up to 10,000 Ukrainians over the coming months.
Since the conflict began more than £2.3bn in military aid has been given by the UK.
The video by Number 10, shows soldiers dressed in camouflage, filing into a building one by one with the Mr Johnson watching on and giving a bystander a thumbs-up.
The PM can later be seen being escorted around the army base as soldiers carry-out a mock hostile situation.
Mr Johnson, who resigned as Prime Minister earlier this month, addresses the camera to voice his support for Ukraine: "I just want you to know, that the people of the United Kingdom support the people of Ukraine and support you in your fight, and I am absolutely convinced that you can win, and you will win."
He finished his opening speech by saying thank you in English, followed by thank you in Ukrainian.
The PM then went into further detail about the programme to help train Ukrainian forces.
"I’ve been meeting some of the 400 Ukrainian troops who are here, being trained by our forces, getting ready to go and fight in Ukraine.
"It’s part of a huge commitment we’ve made to train Ukrainian forces. We want to train about 10,000 of them over the next four months.
"That comes on top of the investment we’re making in supporting Ukrainians with weaponry - 6,900, anti-tank weapons, about 120 armoured vehicles and much much else besides including now, the multiple launch rocket systems that together with the Americans, Germans, and others we’re providing really are starting to make a difference, we hope, to the course of that war, starting to push back Putin’s evil attack on Ukraine.
Mr Johnson continued: "I know that in the end, the Ukrainian people are going to succeed, I know that the Ukrainian forces are going to succeed.
"I’m very proud of the role that the UK has been able to play so far. But in the end, this is thanks to the bravery and the heroism of these Ukrainian troops."
The video ends with a shot of Boris Johnson standing among the soldiers, whose faces have all been blurred to protect their identities.
Johnson shouts 'long live Ukraine' and the screen fades to black.
Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To know...