They couldn't fight, they were in Iranian waters without permission.
Imagine the international incident that would arise if a Chinese patrol boat entered into U.S. territorial water off the coast of California then opened fire on the U.S. Coast Guard ship that tried to intercept them..........Both cases would be considered an act of war.
Post 35. . .as I don’t accept the allegation they drifted/wandered within 3-miles of the Iranian coast-line. Post 35 explains why.