United States Escalates “DeSoto” Patrols in the Gulf of Tonkin

Since the 1950s the U.S. Navy and Marine Corps have periodically carried out covert electronic intelligence missions. These missions are intended to intercept radar, radio, and other electronic transmissions with special listening equipment aboard U.S. vessels patrolling off an adversary’s coastline. In 1963, President Lyndon Johnson authorizes a new wave of such missions specifically in the Gulf of Tonkin, codenamed “DeSoto.”

The U.S. Navy begins DeSoto patrols in the Gulf of Tonkin in 1963, aimed at gathering electronic intelligence transmitted by North Vietnam and China. In February 1964, the United States expands these DeSoto missions, and they begin supporting South Vietnamese espionage, sabotage, and other OPLAN 34A operations. Another primary goal is to determine how closely China and North Vietnam are coordinating coastal defense operations against the OPLAN 34A raids. DeSoto patrols also search for Viet Cong smugglers and North Vietnamese vessels carrying arms and ammunition south to supply the insurgency. Both Vietnam and China become aware of the DeSoto patrols, which eventually acquire the additional, unstated goal of proving America’s resolve to support South Vietnam with its vast naval resources.

The destroyers conducting the patrols are based in Keelung, Taiwan. They are required to stay at least four miles off the coast of North Vietnamese territory and at least 12 miles away from any Chinese territory. One destroyer, the USS Maddox, begins a new patrol in late July. The Maddox departs Keelung on July 28 planning to patrol the North Vietnamese coast while eavesdropping on the North’s military communications. South Vietnamese OPLAN 34A raids are scheduled to occur very near where the Maddox will be on July 31.1