To protect Defending the bridge against aircraft , the Americans positioned Placing the largest concentration of anti-aircraft weapons during World War II leading to Causation `` the greatest antiaircraft artillery battles in American history . ''

The coral atoll surrounding Surrounding Truk 's islands created Creating a safe harbor where the few points of ingress and egress had been fortified Cause_change_of_strength by the Japanese with shore batteries , antiaircraft guns , and airfields .