The Tunnels of Cu Chi by Tom Mangold & John Pennycate ISBN 030436715
200 miles of tunnels around Saigon that not only enabled the Viet Cong to move about undetected but also contained hospitals, training facilities and living quarters. This is the story of the Tunnel Rats, the GIs who fought the VC underground, usually in the pitch dark, and their adversaries, the Vietnamese who saw the US as an invader propping up a corrupt regime.
A fascinating read that doesn't need any dramatic licence to convey both the tactical problem it posed and the claustrophobic terror in overcoming it.