USCGC Blackthorn (WLB-391) was a 180-foot (55 m) seagoing buoy tender (WLB) which sank in 1980 after a collision with teh Tanker Capricorn near the Tampa Bay Sunshine Skyway Bridge, resulting in 23 crew member fatalities.
Damage to the Blackthorn from the initial impact was not extensive. However, Capricorn's anchor was ready to be let go. The anchor became embedded in the Blackthorn's hull and ripped open the port side above the water line. Then as the two ships backed away from each other, the chain became taut. The force of the much larger ship pulling on it, caused Blackthorn to tip on her side until she suddenly capsized. Six off-duty personnel who had mustered when they heard the collision alarm were trapped inside the ship.
Several crew members who had just reported aboard tried to escape and in the process trapped themselves in the engine room. Although 27 crewmen survived the collision, 23 perished.