A further 350 British troops are to be sent to Poland, as tensions over Russia's military build-up on its border with Ukraine continue.
According to the Ministry of Defence, Royal Marines from 45 Commando will work with Poland on "joint exercises, contingency planning and capacity building".
Defence Secretary Ben Wallace said the deployment will send a strong signal that the two countries "stand side by side".
It falls under a bilateral arrangement between the two countries, outside of any NATO commitments.
Speaking at a joint press conference in London with Polish Defence Minister Mariusz Blaszczak, Mr Wallace said they would add to 100 Royal Engineers already in the country since a border crisis with Belarus arose in 2021.
As Russian forces continue to gather at the Ukrainian border, Mr Wallace spoke highly of allied co-operation and planning in case Russia make the "foolish mistake" of invading a sovereign country.