On 7 January 1967, in what is still a heavily classified operation, Secord directed the only successful prisoner of war rescue of the Vietnam War, the Ban Naden raid. A team of the CIA's hill-tribe mercenaries was inserted out of hearing of the POW prison; their surprise raid quickly wiped out about 40 guards. It was then discovered there were about twice as many prisoners as expected. Nevertheless, a scratch force of nine single-piloted Air America H-34 helicopters dropped into the middle of the Hồ Chí Minh Trail and rescued 53 Asian prisoners. This rescue is still used as a case study in CIA training for covert operations.