On finishing high school, Haviv joined the Palmach, the elite fighting force of the Haganah as a condition for being allowed to study at university, as the Jewish Agency obliged all Jewish high school graduates to spend a year either working on a kibbutz or serving in the Palmach.
Haviv took part in the Acre Prison break on May 4, 1947, in which Irgun fighters raided Acre Prison to free Jewish underground prisoners.