Vietnam saw few “traditional” minefields due to the strength of the U.S. Navy’s 7th Fleet, and North Vietnam’s lack of a Navy. The Viet Cong acquired one Korean War vintage MKB moored mine (1,200lb) and set it afloat In December 1966 in the Long Tau shipping channel (Saigon River). Spotted bobbing in the river, the Navy was alerted, and an EOD Diver was dispatched to disarm this Russian mine on 12-31-1966. These same Russian moored contact mines, captured at Wonsan, North Korea in the early fifties, had been used to train generations of EOD personnel at Indian Head, MD HQ, and now at EOD HQ EglinAFB, FL.
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.