What did the SEAL's do in Vietnam?

US Navy SEALs were a smaller force than the US Army's Special Forces (Green Beret); they probably never numbered more than 400 men during the whole war. Nearly 50 SEALs were killed in Vietnam; compared to over 800 Green Berets killed during the war. SEALs were primarily instructors (advisers) and covert operators specializing in blue and brown water (riverine) training and operations. The SEALs paralleled the Army's SF units; minus the "blue & brown" water operations.