As reinforcements arrived in Southeast Asia in response to the North Vietnamese invasion in Spring 1972, President Nixon gave the military authority to start a new bombing campaign. Operation Freedom Train was a limited air campaign that commenced on 5 April against North Vietnamese supply lines below the 20th parallel. Unlike during Rolling Thunder the planners of the new campaign were given much more freedom to prosecute the war and were not micro-managed from the White House. The campaign expanded quickly and by the middle of April Washington was allowing air strikes above the 20th parallel and close to Hanoi and Haiphong. It was during Freedom Train that SAC’s B-52s flew their first missions north of the DMZ on 9 April when 15 aircraft bombed railway and POL targets at Vinh and the big bombers flew their first mission into Route Package VI on 16 April. Freedom Train operations were terminated on 7 May. In this and in other respects, Freedom Train, limited though it was in scope, was the forerunner of the more extensive Linebacker campaigns that followed.