Hmmm I just found that he did do 2 tours, the first was aboard the USS gridely in the tonkin gulf. no battle involved
February 9, 1968 – USS Gridley departs for a Western Pacific (WESTPAC) deployment, to engage in operations in support of the Vietnam War. Ship spends time in the Gulf of Tonkin off North Vietnam, at Subic Bay in the Philippines and in Wellington, New Zealand.
May 27, 1968 – USS Gridley sets sail for the US.
June 6, 1968 – Kerry arrives in Long Beach the day after Senator Robert F. Kennedy is killed in Los Angeles.
From Kerry's own website. It is stretching it to call about four or five weeks in the Gulf of Tonkin on plane duty a "tour." It is just like all the other exaggerations of fact in Kerry's mind.