150 Light Dragoons are heading for Poland as part of Britain’s biggest mission so far since Afghanistan.
This journey will take the armoured convoy more than a week to reach the north-east of Poland from US barracks in Bavaria.
5 RIFLES already lead one of three multinational battle groups in the Baltic States.
Now the Light Dragoons have joined a 1,100 strong American-led force.
The force will be based only 100 miles from Russian territory.
It is NATO's response to growing tension after Moscow's annexation of Crimea. The soldiers hope to reassure allies now fearful of Russia.
Brigadier General Timothy McGuire is the US Army's Deputy Commander in Europe, he spoke to the soldiers shortly before their departure and said:
"This is no invasion force but if necessary it will deter threats".
It's a sentiment echoed by the American-led battlegroup's commander Lt Col Steve Gventer, who also addressed the troops saying:
"You never start a fight but you always finish it. We'll always be prepared to do that but that's not our desire".
To work with the Americans the Light Dragoons have had to make changes.
Radios have been adapted and soldiers now even talk differently. For example, they will not be using acronyms, but instead spelling things out for everyone to understand.
The Light Dragoons are expected to remain in Poland for six months with one main aim, to establish what NATO calls an enhanced forward presence in eastern Europe.