A top-secret study, commissioned by presidential assistant Henry Kissinger, is completed by the office of the Chief of Naval Operations. Code-named Duck Hook, the study proposed measures for military escalation against North Vietnam. The military options included a massive bombing of Hanoi, Haiphong, and other key areas of North Vietnam; a ground invasion of North Vietnam; the mining of harbors and rivers; and a bombing campaign designed to sever the main railroad links to China. A total of 29 major targets in North Vietnam were pinpointed for destruction in a series of air attacks planned to last four days and to be renewed until Hanoi capitulated. This plan represented a drastic escalation of the war and was never ordered by President Richard Nixon. However, Nixon did order certain elements of the proposal, such as the intensified bombing of Hanoi and Haiphong and the mining of North Vietnamese harbors, in response to the 1972 North Vietnamese Easter Offensive.