Will mark check all that apply. which of the following is true of the gulf of tonkin incident? a. it led to the escalation of u. s. involvement in the vietnam war. b. it involved a north korean attack on two u. s. destroyers off the coast of north vietnam. c. there was some doubt as to the facts surrounding the incident, including whether the attack had actually occurred at all. d. the u. s. congress voted to pass the gulf of tonkin resolution by an extremely narrow margin.