A squadron of 14 tanks called the "Challenger 2" will deploy to the conflict in the coming weeks.
But what is the Challenger 2 and what kind impact can it have on the war?
The Challenger 2 is what's called a main battle tank, or MBT, and it's specifically designed to attack other tanks and armored vehicles, seen here during NATO exercises two years ago.
Until now Ukraine's military has primarily relied on its older, Soviet-era tanks. It's also captured and re-purposed some of Russia's during the invasion.
President Zelenskiy has long pleaded with allied countries to include their tanks in aid packages, but some Western officials have been cautious over the concern that Russia or even China could get their hands on advanced Western military technology.
Moscow is also likely to see the introduction of Western tanks onto the battlefield as an escalation of the war and NATO is desperate not to be drawn more directly into it.
The Challenger 2 has been in service with the British army since 1994 and has been deployed to Bosnia, Iraq, and other crises.
The UK's gift could put added pressure on other NATO countries, particularly the U.S. and Germany, to give their own tanks, which have so far resisted.
Along with the Challenger 2, Britain is also giving Ukraine about 30 artillery vehicles called the "AS-90."
It will take time to train Ukrainian forces on how to use the British tanks and artillery, and Russia's London embassy is dismissing the development.
The embassy says the Challengers are unlikely to turn the tide of the war, will drag it out, and will be targeted by Russia's own forces.
