Crossing the Rubicon

This antiwar story takes place in 1967-68 in Vietnam. It is about those who crewed the helicopters in an assault helicopter company. There are two main male characters, one poor and one slightly upper middle class. They arrive in their new company on the same day and therefore become friends. Both are 24 years old. There is also an American female character who is in Vietnam with the Red Cross at the beginning of the book but has to return home when her father becomes ill. Her letters to Robert give a female point of view about the war. She is 23.