[3] The ship was originally named for the unusual Externsteine rock formation investigated by Heinrich Himmler for evidence of cultural significance to early Teutonic folklore and history.

[4] She was employed as a weather observation ship off Shannon Island on the northeast coast of Greenland[5] to aid forecasting of storm events tactically significant to North Atlantic and European combat operations, but was captured on the night of 15 October–16 October 1944 by the American icebreaker USCGC Eastwind.

[6] On 2 October, a Grumman J2F Duck aircraft from USCGC Eastwind spotted a trawler camouflaged in a field of unconsolidated pack ice off North Little Koldewey Island, where the Germans had set up a weather station.

The search for Externsteine was delayed by the weather, but on 14 October she was found trapped in ice 10 nautical miles (19 km) off Cape Borgen.

At 21:00 on 15 November, USCGC Eastwind located Externsteine at a range of 7 nautical miles (13 km) of her radar, and "battle stations" was ordered.

Captain Thomas decided to attack at a range of 2 nautical miles (3.7 km), USCGC Southwind was also present, and illuminated the target with her searchlight.

[7] The captain of Externsteine later told his captors that he thought the attack was being carried out by tanks, and he was amazed that the ships could break through the ice at the speed they did.

[1] Externsteine was the only enemy surface vessel captured by United States naval forces during World War II.