The first British troops have arrived in Estonia as part of NATO's response to Russian aggression.
The 120 soldiers from 5 Rifles left RAF Brize Norton in Oxfordshire and landed at Amari airbase southwest of Tallinn on Friday night.
They will set up an HQ in the country before the remaining troops arrive next month.
There will be 800 British troops in total, backed up by a smaller French force.
Three hundred vehicles, including Challenger tanks and Warrior infantry fighting vehicles, are also en route for eastern Europe.
The troops are part of a NATO move to reinforce its eastern flank in a bid to deter a militarily resurgent Russia
The Defence Secretary, Sir Michael Fallon, said this deployment was to counter an "increasingly assertive Russia".
"NATO is stepping up its commitment to collective defence," he said.
"British troops will play a leading role in Estonia and support our US allies in Poland, as part of wider efforts to defend NATO."
The troops have been warned before travelling to be careful of any Russian attempts to discredit their presence in Latvia.
There are worries that phones might be tapped.
The Ministry of Defence has also been embarrassed by revelations that British soldiers posted in Estonia were provided with a guidebook that included locations of the best strip clubs.
The UK is taking the lead in Estonia and will be backed up by French troops this year, and Danish partners in 2018.
The United States has deployed soldiers to Poland, Germany is sending troops to Lithuania and Canada is taking the lead in Latvia.
The Commanding Officer of 5 Rifles, Lieutenant Colonel Mark Wilson, said: "The UK and Estonia have a long and proud history of serving together, including in Afghanistan, so it is an honour to lead 5 Rifles on this deployment as part of NATO's enhanced Forward Presence.
"My soldiers are looking forward to again be working, training and exercising alongside their Estonian counterparts." (Sky News)