The Coast Guard worked closely with the Navy during Vietnam. For example, at one point, Navy Underwater Demolition Team-13 was being led by Coast Guard Lt. Cmdr. Paul A. Yost Jr. when they were ambushed.
Operation Silver Mace II
The Viet Cong attacked the 13 swift boats damaging a few and killing the American and Vietnamese troops aboard. The Viet Cong also separated the final boat from the rest.
Yost was not about to leave that vessel behind. Instead, he took his boat plus another back to where the boats were being attacked to rescue them.
The boats were all a part of Operation Silver Mace II. Their mission was to stop the Viet Cong movement in a specific section of Vietnam. The swift boats were to carry the troops to shore and give additional support from the water.
Five out of the thirteen were able to make it to their insertion point without any issues. The rest were to head further upriver to let off their marines.
One of the U.S. Marine majors, an advisor on the mission, asked to go up a mile further to drop off the Vietnamese marines. No one had seen any Viet Cong in the area, so Yost said yes.
Yost wanted to have backup in place, just in case, so he asked for the two Seawolf helicopters to launch from a nearby ship and head to their location. However, his request was vetoed by Navy Capt. Roy Hoffman Yost's superior, but Yost was never told.
Not long after the request was made, the eight boats were attacked by claymore mines, rockets, and gunfire. Yost's boat was second in line, and he had it keep going through the kill zone.
PCF-43 was the last boat in line and apparently was in dire need of repairs, and it moved very slowly. The 800 pounds of gear & munitions aboard did not help the situation. As it struggled along, it was left behind in the kill zone.
Yost took PCF-31 and PCF-5 back to the PCF-43, and under heavy fire, he evacuated the injured and dead soldiers. He was able to get away with 15 soldiers and two men that had died. PCR-43 ended up exploding a couple of hours later. For his heroism, Yost was given the Silver Star, and in 1986 he was promoted to the Commandant of the Coast Guard.