But for tanks to be "game-changer", 300 to 400 of them would be needed, an adviser to Ukraine"s defence minister told BBC Radio 4"s Today programme."The sooner we defeat Russia on the battlefield using Western weapons, the sooner we will be able to stop this missile terror and restore peace," Yuriy Sak said.Speaking on the same programme, Nato Secretary General Jens Stoltenberg said sending tanks to Ukraine would make a big difference to the country"s ability to win the war.