What is the author's tone in The Killing Zone: My Life in the Vietnam War by Frederick Downs?

The setting of the book is the nation of South Vietnam, which is part of Vietnam, a former French colony. There is a pro-communist rebellion in South Vietnam, headed by the Vietcong; additionally, forces from North Vietnam have infiltrated the South. The author, Lt. Downs, flies into Vietnam in early September 1967. He is placed in a military unit, under the I and II Corps in the Central Highlands, headquartered in Pleiku. From there, Lt. Downs is sent to Duc Pho, further north and on the coast, by the coastal highway 1. His assignment is to lead a platoon guarding 3 bridges on Highway 1. In the bridge area, there is killing of Vietcong and violence, but the American soldiers seem pretty confident.