In an effort to put pressure on both North and South Vietnam during the negotiations, President Nixon ordered a series of air raids on Hanoi and Haiphong, codenamed Operation Linebacker II. The operation ended on 27 January 1973, after 12 days with heavy casualties and destruction. Both the U.S. and North Vietnam then agreed to sign the Paris Peace Accords that had been proposed in October. South Vietnam objected, but had little choice but to accept it. Clearly, the advantage had been given to Hanoi.