More than 100 reservists from 4 Mercian were put through their paces in Lithuania as they took part in Exercise Iron Wolf earlier in the year.
It is the country's largest military exercise, and involves British, German, Estonian and Lithuanian forces.
Lithuania is the largest of the three Baltic republics.
Just over a decade after it regained its independence during the collapse of the Soviet Union in 1990, Lithuania was welcomed as a NATO member in 2004.
Around 4,000 soldiers took part in Exercise Iron Wolf 2019, including 4 Mercian, who deployed earlier in the year.
"For all soldiers, both regular and reserves, the chance to train with our NATO allies is always hugely valuable," explained Defence Attache to Lithuania, Major Thomas O’Boy.
"Lithuania has a huge amount of expertise, and so do our German colleagues, our Dutch colleagues and all the others who make up the Enhanced Forward Presence battlegroup out here.
"The Iron Wolf Mechanised Infantry Brigade is the prime fighting force of the Lithuanian Army."
The Iron Wolf is a mythological figure in Lithuanian culture.
"[It] called out to Grand Duke Gediminas, who founded Vilnius, in a dream, and inspired him to found it here," Major O'Boy added.
NATO has been beefing up its presence in Eastern Europe for years.
There are 1,000 British troops in Estonia as part of the plan drawn up after Russia annexed Crimea and sent troops into Eastern Ukraine.
"This exercise is a way for us to show just how ready for the fight our Enhanced Forward Presence battle group is, as well as the mechanised Iron Wolf Brigade from the Lithuanian armed forces," Major O'Boy explained.
While Lithuania sees Russia as the main threat to the country, Exercise Iron Wolf is, as Major O'Boy remarked, not confrontational.
"It is competitive between two highly capable forces."
Lithuania's entire military consists of 19,850 serving personnel - 12,400 in the Army, 750 in its Navy, 1,200 in the Air Force, and 5,500 other troops.
The UK's Ambassador to Lithuania told Forces News there is a wide range of relationships between the two nations, with 10% of the Lithuanian population living and working in the United Kingdom.
"[The defence relationship with Lithuania] is absolutely vital," Ambassador Brian Olley said.
"Lithuania and the Baltic states have been invaded many times over the centuries and they play a very important part in terms of a member state of the European Union.
"Clearly, the level of deterrence which NATO is able to provide in the Baltic countries is very significantly increased by the presence of British troops," he added.
The continued presence of British troops on exercises like Iron Wolf is an attempt to show support and to work at continuing to strengthen the defence relationship.
Major Rimas Cepononis, Commander, Exercise Iron Wolf, told Forces News, "actually, it's not so challenging when you do it with the nations like the British.
"We are both NATO countries, we have very similar, or sometimes the same, procedures and same communications, weapons we know each other."
As reservists, it is not often the troops will experience such intense fighting, and realistic simulations of mine fields and other threats.
Major Nigel Bradley, 4 Mercian, said: "The learning curve on this exercise is massive, so our preparation was on really small training areas back in the UK. This is a huge step up."
Not everyone makes it through unscathed when split-second decisions go wrong.
For Private Martin Chomanicz of 4 Mercian, it has been an invaluable experience: "I've been tested to the max personally, it's where you find out where you really are aren't you.
"If you get to the edge, keep pushing."
"[It has been] cold, wet, training's a bit iffy, to be honest, but managed to get through it.
"[I have been] really enjoying it, it's something different for me.
"My job mainly involves sitting in an office looking at a computer screen, so this is a nice little break from it to be honest."