The troops have been deployed to reassure allies fearful of Russia in what Forces TV called 'Britain’s biggest mission since Afghanistan.'
The 150 Light Dragoons have joined a 1,100 strong American-led forces which will be based just 100 miles from Russian territory.
In total at least 1,350 American, British and Romanian soldiers have been sent to Poland from a base in Germany.
Brigadier General Timothy McGuire, the US Army's Deputy Commander in Europe, spoke to soldiers shortly before their departure reiterating the purpose of their mission.
British troops joined American-led forces as they advance to Poland
He said: “This is no invasion force but if necessary it will deter threats.”
US army commander Lt. Col. Steven Gventer, insisted that the mission was not being treated as a drill by troops.
He said: “You never start a fight but you always finish it.
“We'll always be prepared to do that but that's not our desire.”
The decision from NATO comes as Putin moved missile systems and troops into the Kaliningrad oblast, which borders Poland and Lithuania. The outcrop of Russian territory is a relic of the Soviet Union and is seperated from the rest of Russia by other Baltic states.
Around 4,000 Nato troops have been placed across Poland, Latvia, Lithuania and Estonia.
4,000 NATO troops take part in Lithuania’s largest exercise near Russia’s border Mon, November 28, 2016
Eleven NATO countries have sent 4,000 troops to Lithuania, the largest Baltic nation, to participate in this year’s Iron Sword exercises. The war games are meant to test the country’s ability to rapidly deploy a large number of troops.
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Members of the U.S. 173rd Airborne Brigade fire blanks from a machine gun during a simulated attack
This is no invasion force but if necessary it will deter threats
US army commander Lt. Col. Steven Gventer
A fleet of 300 UK military vehicles are set to be delivered to Estonia including Challenger 2, Titan and Trojan tanks and AS90 self-propelled artillery pieces.
A 450 strong German force has been sent to Lithuania to work alongside Belgian and Danish soldiers in the region.
Defence Secretary Michael Fallon said: “In the face of an increasingly assertive Russia, 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.
“Our rising defence budget means we can support those deployments in the long-term and strengthen our commitment to European security.”