Captain John Robert Cotter served in the Australian Army in Vietnam. He was a combat engineer, tasked with disarming mines, dismantling booby traps, dealing with gas warfare, establishing roadways for infantry transport, and more. He was among the first to discover the tactical importance and vast scale of enemy tunnels, and it was his job to crawl through them in order to map their network, seize supplies, flush out enemies, and place explosives.

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