Blackthorn was one of 39 original seagoing buoy tenders built between 1942-1944. All but one of the original tenders, the USCGC Ironwood (WLB-307), were built in Duluth.
Blackthorn was initially assigned to the Great Lakes for ice-breaking duties, but after only a few months, she was reassigned to San Pedro, California. She served in San Pedro for several years before being brought into the gulf coast region to serve in Mobile, Alabama.
In 1979-1980, Blackthorn underwent a major overhaul in Tampa, FL. Sadly, while leaving Tampa, Bay on 28 January 1980, she collided with the tanker Capricorn. Shortly after the collision, Blackthorn capsized, killing 23 of crew. The cutter was raised for the investigation, but ultimately was scuttled in the Gulf of Mexico after the investigation was complete.
Having just completed her overhaul, Blackthorn was outward bound from Tampa Bay on the night of 28 January 1980. Meanwhile the tanker Capricorn was standing into the bay. The captain, Lieutenant Commander George Sepel was on the bridge, but Ensign John Ryan had the conn. Having been overtaken by the Russian passenger ship Kazakhstan, Blackthorn continued almost in mid-channel. The brightly lit passenger vessel obscured the ability of the crews of Blackthorn and Capricorn to see each other. Capricorn began to turn left, but this would not allow the ships to pass port-to-port. Unable to make radio contact with the tender, Capricorn’s pilot blew two short whistle blasts to have the ships pass starboard-to-starboard. With the officer of the deck confused in regard to the standard operating procedure, Blackthorn’s Captain issued orders for evasive action.
Though a collision was imminent, damage did not figure to be extensive. The problem, however, was that Capricorn’s anchor was ready for letting go. It became imbedded in the tender's hull and ripped open the port side. Just seconds after the slack in the anchor chain became taut, Blackthorn capsized. Six off-duty personnel who had mustered when they heard the collision alarm, were trapped in the dark. Several crew members who had just reported aboard tried to escape and in the process trapped themselves in the engine room. Though 27 crewmen survived the collision, 23 perished. In the end the primary responsibility for the collision was placed with Commander Sepel as he had permitted an inexperienced junior officer to conn the ship in an unfamiliar waterway with heavy traffic.
MARINE BOARD OF INVESTIGATION REPORT ON COLLISION BETWEEN USOGC BLACKTHORN AND TANKSHIP CAPRICORN APPROVED BY COMMANDANT
The Commandant of the United States Coast Guard, Admiral John B. Hayes, has approved the report of the marine board of investigation on the collision between the Coast Guard Cutter Blackthorn and the Tankship Capricorn. The collision occurred in Tampa Bay, Florida, on January 28, 1980, resulting in the deaths of 23 Coastguardsmen.
The board determined that the cause of the casualty was the failure of both vessels to keep well to that side of the channel which lay on their starboard (right) side. In concurring with the marine board’s determination of the cause, the Commandant emphasized in his "Action" that the failure of the persons in charge of both vessels to ascertain the intentions of the other through the exchange of appropriate whistle signals was the primary contributing cause. Additionally, Admiral Hayes pointed out that attempts to establish a passing agreement by using only radiotelephone communications failed to be an adequate substitute for exchanging proper whistle signals.
The collision occurred in the evening of January 28, 1980, near the junction of Mullet Key and Cut "A" Channels approximately three-quarters of a mile from the Sunshine Skyway Bridge in Tampa Bay. The vessels collided nearly head on, and as a result, the port anchor of Capricorn became imbedded in the port side of the Blackthorn. The momentum of the two vessels caused the Capricorn’s anchor chain to become taut which resulted in the capsizing of the Blackthorn. The Capricorn subsequently ran aground north of the channel and the Blackthorn sank in the channel. Twenty-seven of the 50 Blackthorn crewmembers were rescued.
The marine board found evidence of violation of various navigation laws on the parts of the master and pilot of the Capricorn. There were similar findings on the part of the commanding officer and officer of the deck of the Blackthorn. These matters were referred to the commanders of the Seventh and Eighth Coast Guard Districts for further investigation and appropriate action.
The Commandant also acted on various safety recommendations made by the marine board concerning training and equipment aboard Coast Guard vessels, and navigation considerations in Tampa Bay.