american military build—up in poland is a threat to russia's national security. more than 3000 troops, together with tanks and armoured vehicles, are being deployed along nato's eastern front, in the biggest us military reinforcement in europe for decades. 0ur defence correspondent jonathan beale has been watching the american contingent arrive. the americans are coming, back into europe in force. we joined an armoured convoy as it crossed from germany into poland, nearing the end of theirjourney that started in colorado. eagerly awaited in a nation that's been waiting for us support. what signal do you think it will send to moscow? that we are ready to do everything. it's a normal militaryjob to defend a country, to defend family, to defend the world. they came by road and by rail, an entire armoured brigade of 3,500 troops and hundreds of vehicles.