On August 2, 1964, the Vietnam War escalated. President Kennedy was assassinated in November 1963, and was taken over by Vice President Johnson in accordance with the Constitution. This changed the U.S. attitude toward the Vietnam War. Johnson prepared a secret emergency plan to escalate the war, and on August 2, 1964, when two U.S. destroyers were bombed by North Vietnam battleships in the Gulf of Tokyo, he had an excuse for carrying out an emergency plan. The U.S. Senate also granted him the power to help anyone who asked to defend his freedom and resist armed attacks. Therefore, a large number of U.S. troops were sent to Vietnam. In February 1965, the U.S. Army began bombing North Vietnam. In March, the U.S. Navy was prevented from landing as ground troops