First Battalion The Royal Welsh have taken over from the Royal Tank Regiment battlegroup as the lead British battlegroup on NATO's eastern flank.
Both units paraded at a transfer ceremony at Tapa Military Base in Estonia, in front of some of the heavy armour the UK has sent to the region amid Russia's invasion of Ukraine.
The Royal Welsh, nicknamed the 'Welsh Warriors', arrived from their base in Sennelager, Germany, earlier this month.
They brought 900 personnel and dozens of armoured fighting vehicles and Challenger 2 tanks.
The base at Tapa is less than 100 miles from the Estonian border with Russia.
Since Moscow's annexation of Crimea in 2014, NATO has deployed a multinational battlegroup in Estonia.
Despite the Royal Welsh taking over the UK's lead battlegroup, the Royal Tank personnel are staying on to carry out further exercises in the Baltics.
Lieutenant Colonel Ru Streatfeild, Commander, UK EFP (Enhanced Forward Presence) Battlegroup, told Forces News: "People are aware of the importance of what's going on, they see it in the news.
"They understand it's very serious in Ukraine and that gives them a sense of purpose and focus on what they're doing here.
"You need a range of capabilities. We're what's called a close battle, so we have tanks and armoured fighting vehicles."
Watch: The jets defending NATO's Russian border
The parade in Tapa also demonstrated the contribution of some of the UK's NATO allies.
There is a contingent of French mountain troops and 200 Danish soldiers.
This week, the Estonian Parliament called on the United Nations to discuss establishing a no-fly zone over Ukraine.
The country's Minister of Defence Kalle Laanet welcomed the surge of UK troops: "On one hand it is a strong sign to Russia. Second, it is very important also internal in Estonia, that our people see that allies are protecting us, they are sending more troops."