Operation End Sweep - Preparations

Preparations

Under the Hague Convention of 1907, the United States was required to eliminate the mine threat it had created after the end of hostilities. Accordingly, the U.S. Navy's Mine Warfare Force (MINEWARFOR) began planning for removal of the mines as soon as Nixon ordered the mining campaign to begin. In order to ease post-war minesweeping, only mines that could be cleared by magnetic sweeps were used, and the vast majority of mines laid were programmed either to self-destruct or render themselves inert after a specified period of time. Of course, the U.S. Navy also knew generally where the mines had been laid, although the inherent inaccuracy of aerial minelaying meant that the precise location of each mine was not known.

Rear Admiral Brian McCauley became Commander, Mine Warfare Force, and Commander, Task Force 78, in September 1972. Task Force 78 was designated as Mine Countermeasures Force, U.S. Seventh Fleet, and was created for the upcoming minesweeping operation that would become known as End Sweep.

Minesweeping equipment and U.S. Navy personnel trained in minesweeping both were in short supply, so, in order to minimize the danger of mine explosions to American personnel and equipment, Task Force 78 planners devised an operational scheme in which minesweeping was limited to areas in which the mines already had rendered themselves inert. If all mines known to be in area also were known to have passed their self-sterilization dates, Task Force 78 planned to conduct a check sweep of a few passes; if it was not clear that all mines in a given area had become inert, a more thorough clearance sweep was to be used.

In the United States, the Chief of Naval Materiel, Admiral Isaac C. Kidd, Jr., organized a Mine Warfare Program Office charged with controlling scientific and technical support to End Sweep. The program office ensured that resources were allocated to the operation that allowed the rapid development of shallow-water minesweeper gear and precision navigation and locating systems, the latter providing minesweeping forces with an improved capability to determine the configuration of a minefield and to adjust their daily operations accordingly.

Ten ocean minesweepers (MSOs) were assigned to Task Force 78 to sweep deep-water approaches to North Vietnamese ports and inland waterways and to serve as helicopter control vessels. In addition, the tank landing ship USS Washtenaw County (LST-1166) was modified in Japan between November 1972 and February 1973 to serve in End Sweep as a “special device minesweeper,” redesignated MSS-2. As such, she was intended to be used for check sweeps through waters which presumably were clear of active mines to ensure that passage indeed was safe. She was pumped full of polyurethane foam so that she would not sink if she struck a mine, was equipped with padding to protect her all-volunteer skeleton crew, and was modified so that her entire crew of six could remain topside during her minesweeping runs, ensuring that they would be blown overboard if she struck a mine rather be injured or killed by slamming into the overhead anywhere below decks.

The Navy‘s newly created air mine countermeasures capability resided entirely in the CH-53 Sea Stallion helicopters of Helicopter Mine Countermeasures Squadron 12 (HM-12), all of which were assigned to the operation. In addition, one detachment each from the Marine Corps's Marine Heavy Helicopter Squadron 463 (HMH-463) and Marine Medium Helicopter Squadron 164 (HMM-164) provided a total of 24 more CH-53s. The helicopters practiced for the operation off Charleston, South Carolina, where it was discovered that the Marine Corps pilots' inexperience in towing the heavy Mark 105 hydrofoil minesweeping sleds posed a risk to the personnel and equipment involved, a particularly unacceptable risk because of the scarcity and expense of the sleds. As a result, a scientist devised a buoyant, magnetized pipe filled with styrofoam which any helicopter pilot could tow easily. Painted orange, the new device became known as the Magnetic Orange Pipe (MOP).