W.J Miller QMC USN, a writer for the USN All Hands Magazine wrote a nice 6 page story on the AMS minesweepers (136″) and the CoMinRon 3 Boat Division sweepers (36′) - Which were later redesginated as Mine Sweeping Boat Division ONE for the remaider of the Korean War. Following the Korean Armistice in August 1953, the unit became Mine division – 111 homeported in Sasebo. In 1958 it was further redesignated Mine Division – 33 and reorganized to report to COMINRON THREE/MINFLOT 1 Sasebo.

Ed Sinclair

Charlotte Knight, Colliers War Correspondent, produced a nice article (attached) on AMS operations of COMINDIV Three in Korea during a fall 1951 visit to these minesweepers. These were primarily YMS designs of WWII that were converted to Auxiliary Mine Sweepers, and given ship names. The YMS Series (>425) were only given hull numbers during WWII. Fifty keywords of ship names commanding officers and key personnel are also listed in the complete article.

Seawall @ Jake (Juliet) Basin Sasebo, Japan

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The Sasebo, Japan based mine sweeping boat division began as the COMinRon-3 Boat Division sometime following the outbreak of the Korean War in June 1950. In early 1951 it was commissioned as Mine Sweeping Boat Division ONE, still reporting to COMinRon-3, cosisting of two 40′ motor launches and a dozen or more LCVP’s as minesweepers. Conversion to mostly 50′ motor Launches (modified with decks and even cabins, before the end of the war. At the Korean Armistace, the Division was re-named Mine Division 111, reporting to MinRon 11 in Long Beach, CA. In 1958 their 50′ Motor Launch Minesweepers (MLMS) were replaced by newly built 36′ Mine Sweeping Launches (MSL’s) built bt Sagstad Shipyards in Seattle, and powered by Boeing 502-10-C Gas Turbine Engines.

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Edward Sinclair

This video shows Mine Sweeping Boat Division ONE launching Four LCVP Magnetic Minesweepers from the USS Cabildo LSD-16 in April 1952. MSB-1 had a variety of boats, including modified USN Motor Launches (40′ and 50′), and 36′ Landing Craft Vehicle Personnel (LCVP’s) outfitted with Oropesa sweep gear for moored minesweeping. The four LCVP’s outfitted for magnetic minesweeping could not be launched by cranes from the LSD, because the magnetic minesweeping gear was powered by several 750 lb submarine batteries stored in the boat, making it too heavy to launch via the mother ship’s cranes. Therefore, the LSD would ballast down, flooding a portion of the well deck, and the boats would simply sail out via the stern gate. Recovering magnetic boats at night, were the reverse of the process. The LSD ballasted down, flooding the well deck with enough water to float the boats, and the boats would sail into the well deck under their own power.

The magnetic minesweeping tails were approximately 1,500 feet long, with bare electrodes hanging into the water at 1,000 and 1,500 feet, alternately pulsed positive and negative, setting up large and powerful magnetic fields to detonate magnetic mines 1,000+ feet behind the towing boats. This of course was predicated that the minesweepers be as non-magnetic as possible, because they first had to sail past these magnetic ground mines lying on the bottom of the harbor.

The video shows the boats connecting to their mag tails, retrieved from these same boats using sailor-power (by-hand) following the previous days sweep operations and “flaked-down” on the well deck.

Following the magnetic mine sweeping boats, there is an LCVP moored minesweeping boat shown cutting a moored mine. Following the severing of a moored mine cable or chain, the mines float to the surface, and generally are sunk from a safe distance away by gunfire. However, in this video you see two Mine Squadron Three Explosive Ordnance Disposal Officers in a rubber dinghy paddling to these Russian made mines, and disarming then (Rendering Them Safe) for the purpose of exploiting the technology and returning then to EOD Headquarters located in Indian Head, MD during the Korean War. Generations of EOD Divers have been trained to disarm live mines on the dozens of Russian mines captured by Mine Squadron Three Officers in Wonsan, North Korea during our 900 day seige and occupation of this enemy harbor.

In fact, one of these 1,200 lb Russian MKB behemoths was discovered floating down the Long Tao Shipping Channel (Saigon River) on December 31, 1966, and the EOD Diver LtCdr Frank Talarico disarmed the MKC Chemical Horn Mine in the river near the Saigon Port Complex. He tied a rope to an eyebolt in the mine and dagged it to shallow water, he and another EOD person removed the cover plate, and pulled out the detonator and Tetryl booster. Their training at Indian Head kept them alive. The 506 lbs of cast TNT is later steamed out of the 984 lb steel case to for return to EOD HQ.

I apologize for the abrupt end to the video. Evidently, the hosting service truncated the video due to it;s size.

Ed Sinclair

A second major discovery in the use of Russian mines by the enemy in Vietnam, the North Vietnamese hauled segments of the more modern Russian ground mines, the 24″ cylindrical HAT II acoustic-magnetic bottom mines down the Ho Chi Minh Trail, to the Cua Viet River. These have modular sections, and are up to 6 ft long when assembled. One was believed to have exploded and capsized an LCU/YFU full of munitions, killing six of the seven sailors aboard, while traversing the Cua Viet River to the Dong Ha Marine Base upriver.

EOD Divers found another HAT II fully assembled and planted outside the bar at the mouth of the Cua Viet river, and rendered it safe. Luckily, no large USN ships could navigate the shallow Cua Viet River, and did not venture across the bar heading upriver.

It is believed that the North Vietnamese, or like during the Korean War, Russian advisors, assembled these mines, and tied a series of floation devices around or alongside them, swam into the river floating these mines, and deflating the flotation devices with knives to “plant” these ground mines on the river bottom. These mines were believed to have acoustic-magnetic trigger mechanisms.

During the Battle Of Dai Do Village, in the Sring of 1968, Naval forces battling the NVA north of the Cua Viet river spotted suspicious activity on the north bank during the battle, and sent ground troops to investigate later. They discovered segments of these HAT II cylindrical mines on the river bank. EOD divers from the Cua Viet Base discovered parts for eight complete mines, evidently hauled down the Ho Chi Minh Trail in peices by the North Vietnamese. This was the NVA attempt to close down the Dong Ha-Cua Viet ammo supply line, and overrun the USMC Base at Dong Ha. MSL’s from the USS Epping Forest left Da Nang the day this discovery was made, and sailed north to Cua Viet, prepared to sweep the river. This minesweeping unit consisting of ten 36′ Mine Sweeping Launches, now designated as the Epping Forest Boat Division, formerly Mine Division 33, had moved aboard the USS Epping Forest permanently in the summer of 1966. They allegedly towed a WWII “iron rail” magnetic sweep, believed to be a section of magnetized railroad track, packed inside a PVC pipe, behind their 36′ Mine Sweeping launch. No detonations resulted from their sweeps of the Cua Viet, the scene of the deadly LCU/YFU explosion days earlier.

Almost all remaining mine planting activity in Vietnam in Bays and Rivers consisted of home made explosive devices, manufactured in the jungle from unexploded US ordnance explosives, trash, and battlefield junk such as tin cans, shell casings, aircraft wing tanks, and various containers. The most frequent were command detonated explosives planted in the rivers, and detonated by an enemy fighter from a foxhole alongside the river, using dry cell batteries.

Since two brutal recessions have interfered with my ability to finish researching and writing more of the book (I needed to find employment as a result) the book research and writing have been limited, but I am still gaining more information as people read this article. I am planning on starting with a website which gives me the ability to share thousands of items that cannot be included in a book.

I may be contacted for information, or unique contributions of photos, memorabilia, documents, or any anecdotes you would feel worthy – in telling the history of small boat minesweeping.

Ed Sinclair – 2011