British troops have arrived in Estonia as part of a major Nato mission in the Baltic states to deter Russian aggression.
Around 120 soldiers from 5 Rifles landed at the Amari airbase on Friday, south-west of the capital Tallinn.
There will eventually be 800 British troops stationed in the country as part of one of the biggest deployments to Eastern Europe in decades.
The first troops deployed will set up a UK headquarters in the country before the rest arrive next month.
UK troops will work alongside French and Danish forces to "provide a proportionate, defensive, and combat capable force to defend our Nato ally and deter any form of hostile activity against the Alliance", the Ministry of Defence said.
Britain is taking a leading role in the Estonia Battlegroup, while other nations are deploying troops to Latvia, Lithuania and Poland as part of Nato's Enhanced Forward Presence battalion.
Defence Secretary Sir Michael Fallon said "Nato is stepping up its commitment to collective defence".
"British troops will play a leading role in Estonia and support our US allies in Poland, as part of wider efforts to defend Nato.
Lieutenant Colonel Mark Wilson, Commanding Officer of 5th Battalion The Rifles, 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."
Around 300 UK vehicles were also transported from the UK this week by ferry headed for Estonia, including Challenger 2 tanks, Warrior infantry fighting vehicles, and AS90 self-propelled artillery pieces.