In early 1967, Brigadier Stuart Graham, the new Australian Task Force Commander, drew up plans for a barrier minefield which he believed would sever a vital Viet Cong supply route, preventing their movement from their mountain bases to the rice-growing areas in the west and protecting local villagers from communist influence. It would contain approximately 20,000 'jumping jack' mines between two wire fences for a length of 10 kilometres, from the Horseshoe near Dat Do to the coast. Sappers of the Royal Australian Engineers would lay the mines, fitted with anti-lift devices, and the completed minefield would be guarded by Task Force and Army of the Republic of Vietnam (ARVN) troops.
On 25 May 1967, the 1 Field Squadron Operations Log reported:
Mines laid today 1348. Total mines with anti lift 2088. Total mines without anti lift 1148. Grand total 3236.
[AWM 95 Item 1 Field Squadron RAE Ops Log, May 1-31 1967]
There were a number of injuries and deaths during the mine-laying operation and casualties continued after its completion. The minefield's security was ineffective and the Viet Cong breached the barrier fences, lifted the mines and re-used them against the Australian and ARVN troops.
They were very clever. They would set a mine, for instance an M16 mine; they were pulling them up from our minefield. Pulling a pin out of a grenade and sitting down, under the ground, and sitting the mine on top, the M16 to keep the grenade loaded and fill it in. When we'd come along we'd see the mine and unscrew the mine. Make it safe at the top; unscrew the detonating device out of it. Lift the mine out and, when we did, the grenade would go off.
[Sapper Robert Earl, MID, in Michael Caulfield, The Vietnam Years, Hachette Australia, 2007, p 193. Drawing on Interview No: 639 in the Australians at War Film Archive]
Sapper Robert Earl, 1st Field Squadron, Royal Australian Engineers, suffered serious injuries while he was assisting 5RAR troops with a 'dustoff' casualty evacuation in the Long Hai hills during the night of 4 July 1969. He and the 5RAR casualties were 'casevaced' out to Vung Tau.
The choppers came in then to pick us up. They were still transporting out the wounded. It was an M16 jumping mine… they had put a snail on top of the three prongs, so all you would see was a snail. A snail… in daylight you wouldn't see it. In fact, I think it would encourage the blokes to walk on the snail anyway.
[Sapper Robert Earl, MID, in Michael Caulfield, The Vietnam Years, Hachette Australia, 2007, p 188. Drawing on Interview No: 639 in the Australians at War Film Archive]
In August 1969, during Operation Esso, a 5RAR attack in the Long Hai mountains, fifty-eight Australians were wounded and nine killed. Most of the casualties were the result of jumping jack mines.
Details of the minefield had been kept from the Australian public but the continuous stream of minefield casualties prompted public controversy and some difficult questions in Parliament.
In 1968, Australian engineers began the dangerous task of sweeping and clearing the 'barrier minefield'. Their success was limited until late 1969 when Major Rex Rowe, the commanding officer of 1st Field Squadron, Royal Australian Engineers and his colleagues devised a solution. Attaching large steel-plated rollers to the rear of an armoured personnel carrier (APC), they were able to trigger mines more safely. It took nearly two years to clear the mines from the field. By then, the Australian mines had contributed significantly to the Australian casualty rate in Vietnam.