Thousands of South Korean troops, backed by dozens of attack helicopters, today staged an exercise near the tense border. <br/><br/>A spokesman for the Joint Chiefs of Staff said this drill was aimed at thwarting a simulated attack by North Korea. <br/><br/>The show of military strength included about 50 tanks and armoured vehicles, which crossed a floating bridge backed by dozens of attack helicopters and self-propelled guns. <br/><br/>It was the biggest drill since cross-border tensions flared over the sinking of a South Korean warship on March 26 and follows an anti-submarine exercise by the South's navy last week.