Hundreds of British soldiers have undergone intense training in freezing conditions as part of NATO's presence across the Baltic region and Poland.
The 5 RIFLES-led NATO enhanced Forward Presence (eFP) Battlegroup faced deep snow and temperatures as low as -20C during the two-week Exercise Winter Camp in Estonia.
Lieutenant Colonel Jim Hadfield, Commanding Officer of the NATO Battlegroup, said the eFP Battlegroup has to be "combat credible".
"Combat credibility for me is the function of three things; one is our integration, and that's not only our integration into the Estonian national defence plan, but our integration across the whole region," he said.
"It's also about interoperability [and] our ability to soldier in this environment alongside our Estonian colleagues."
To prepare them for Exercise Winter Camp, the battlegroup took part in a cold weather operator's course.
This included learning to build shelters, staying out in conditions well below freezing and surviving jumping into ice-cold lakes.
Lt Col Hadfield said this course is used as the the "vehicle" to prepare troops for unfamiliar conditions.
"Whether it's a jungle environment, desert environment or it's an extreme cold environment it forces you to become very, very competent at doing the basics extremely well and we've learned that over the last couple of months," he said.
"As British soldiers, we don't often soldier in -20C or this kind of depth of snow.
"It presents equipment challenges, clothing challenges, as well as different tactics, and the cold weather operator's course provides that foundational baseline bit of training to make sure that we can… be as good a team as we can be."
The infantry companies of 5 RIFLES honed their fighting skills in dense, snowy forestry with a combination of dismounted close combat, live and blank fire tactical training.
It is hoped the exercise will demonstrate combat readiness and strengthen the working relationship with Estonia for future NATO operations in the region.
"In terms of tactics, techniques and procedures, they do things differently in some areas and, as always, we're constantly looking for ways to make ourselves better," said Lt Col Hadfield, adding that both nations' militaries will adopt effective methods from one another.
Major Rob Fellows, Officer Commanding of A Company, 5 RIFLES, said he had never operated in "conditions as challenging as this".
"We all joined the infantry for a challenge, and this absolutely qualifies as one," he said.
Meanwhile, the Challenger Main Battle tanks of D Squadron Queen's Royal Hussars tackled the snow and ice of forest tracks as they trained with the Estonian Defence Force's (EDF) Scouts Battalion.
Trooper Cameron Dixon, D Squadron, said it was "by far" the coldest exercise he had taken part in: "You've got to keep warm, eat hot food and move about while maintaining the tanks.
"You've got to keep layered up too and it can be quite tight inside the tank with body armour on, but you've got to push through."
All the training was supported by personnel from the Royal Electrical & Mechanical Engineers (REME), the Royal Logistic Corps, 5 Armoured Engineer Squadron part of 22 Engineer Regiment, as well as medics.
UK Armed Forces have kept a rotating presence in Estonia since 2017, with troops taking on a leading role in NATO's response to a developing threat from neighbouring Russia.