Russia's 'Doomsday Radio' has singled out a NATO state in what could be seen as a threat to the alliance in a fresh burst of coded messages. One of the messages broadcast by Vladimir Putin's mysterious radio station simply read LATVIA - the allied state which shares a 170-mile border with Russia . Latvia, along with its neighbours Estonia and Lithuania are all seen as vulnerable to Russian invasion. If Russia were to invade, NATO's article 5 would be triggered, and likely, World War 3 . The