British Army soldiers from 1st Battalion The Mercian Regiment are undergoing final preparations at Sennelager Training Ranges in Germany, ahead of deployment to Estonia next month.
Eight hundred British service personnel are taking part in Exercise Tallinn Dawn before leading a NATO battlegroup alongside French soldiers as part of Operation Cabrit.
Op Cabrit is one of the Army's key missions – it aims to defend NATO's eastern flank against an increasingly assertive Russia.
UK personnel have been in the Baltic nation on Operation Cabrit for the past four years.
Troops are restricted to the Sennelager training facility and banned from the outside world.
All visitors have to be tested, making Exercise Tallinn Dawn the most ambitious training yet due to stringent German and British COVID restrictions.
Soldiers have been repeatedly tested even before the exercise began in Germany.
Brigadier Paddy Ginn, Commander 20th Armoured Infantry Brigade, told Forces News: "It’s really hard, but we've done it, and we're absolutely abiding by all of the German regulations and all of the British regulations. Very strict testing regime.
"We've tested over 3,500 people using both lateral flow testing and also PCR [polymerase chain reaction] testing.
"We're also householding, we're also bubbling, we're also ensuring people are wearing their masks and we're abiding strictly by the hands, face, space regulation."
Exercise Tallinn Dawn is seen as a pilot for conducting military exercises during a pandemic as well as proving Sennelager as a launchpad for European operations.
Brig Ginn added: "Being in continental Europe, being in the heart of Europe, being in Germany and being able to work alongside our German partners again, NATO allies; absolutely vital.
"Germany is perfect as the springboard for operations within Europe and we're demonstrating that.
"Germany as a unique training environment matches the environment we could be operating in – on the eastern flank of NATO.
"Matching training with operating environment is vital for the British Army. Train as you would fight," he added.
Commanders say COVID has presented hurdles but hasn't diminished the training.
A wide variety of topics are covered on the syllabus, from disinformation and fake news to full-blown warfighting.
However, the restrictions have meant the whole of B Company has gone into isolation because of a couple of positive coronavirus test results.
"[This has meant] Dragon Company, our support company, have now re-rolled and they are doing some of B Company's jobs whilst they are now a fighting company as well as their own support company," Sergeant James Clayton, 1 Mercian Battlegroup Headquarters said.
Sergeant Tupou Veiogo, Royal Electrical And Mechanical Engineers, added: "It's very restricted right now even within crews, within the squadron, so for you to visit or go pass a message on to another crew, you have to make sure that you remain at the correct social distance and wear the correct face protection and all that good stuff.
"We know that everyone's been tested negative now three times already so, us contained within our own little squadron bubble now, we can rest assured that we are all safe."
After being locked down for much of 2020, soldiers are relieved to be outdoors and training again.
"We're all clear and there's no restraints on us deploying straight away but at this moment in time morale is very high," said Sergeant Josh Maybanks, 3rd Regiment Royal Horse Artillery.
"The guys are good, they've got the supplies, they've got the rations, ammunition, so we're good."
In November, 1st Battalion The Mercian Regiment were the first British soldiers to return to the Sennelager Training Ranges in Germany since the outbreak of the coronavirus pandemic in March 2020.