USCGC Blackthorn (WLB-391) was a 180-foot (55 m) seagoing buoy tender (WLB) which sank in 1980 in a collision near the Tampa Bay Sunshine Skyway Bridge, resulting in 23 crew member fatalities. An Iris-class vessel, she was built by Marine Ironworks and Shipbuilding Corporation in Duluth, Minnesota. Blackthorn's preliminary design was completed by the United States Lighthouse Service and the final design was produced by Marine Iron and Shipbuilding Corporation in Duluth. On 21 May 1943 the keel was laid, she was launched on 20 July 1943 and commissioned on 27 March 1944. The original cost for the hull and machinery was $876,403.