Five of the UK's Apache attack helicopters have been deployed to Estonia as a deterrent to a "very credible threat" from Russia.
Defence Secretary Gavin Williamson watched the aircraft take off from Wattisham Airfield in Suffolk.
They will form part of NATO's enhanced forward presence (eFP), which was established to deter potential aggression from the Kremlin, during their three-month deployment.
Mr Williamson, speaking at the airfield, said: "It's a very credible threat that we see from Russia and part of the reason that we're deploying five Apache attack helicopters is making sure that we're constantly adapting to a changing situation, but this is about deterrents.
"This is about NATO nations standing together in unity as one and you see Great Britain playing the largest role in enhanced forward presence with the largest number of service personnel deployed.
"The enhancement of that deployment with the Apache attack helicopters is really vital and very, very important and it's been very warmly welcomed by so many nations."
The Apaches will be supported in Estonia by Wildcat battlefield reconnaissance helicopters.
A further 110 UK personnel have been deployed to the Baltics as part of Operation Cabrit, taking the total there to around 1,000.
Major David Lambert, commanding officer of 663 Squadron, 3 Regiment Army Air Corps, said the Apaches would take part in training exercises across the Baltic states while deployed to Estonia.
One of these, called Exercise Iron Wolf and taking part in Lithuania, will involve up to 14 nations.
"Whenever you go somewhere new, there's always things that you learn about how to operate," said Maj Lambert.
"Your fieldcraft needs to change and in the UK we train very much in rolling countryside, it favours us in what we do.
"Actually putting ourselves in a really flat area in close proximity to the Russian border brings some new, complex challenges that we need to look at.
"I'm really excited by the whole prospect."
The creation of the ePF was decided at the Warsaw Summit in July 2016 amid concerns about Russian activity after its annexation of Crimea from Ukraine in 2014.
The eFP is a deployment of defensive but combat-capable forces in countries which include Estonia, Latvia, Lithuania and Poland.
There are four multinational battlegroups across the region, led by Britain, Canada, Germany and the United States which aim to deter any potential Russian aggression.