The ship was built in 1943–44 as yard number 570 by P. Smit, Jr. Shipyard, Rotterdam, South Holland, Netherlands. Originally intended to be the trawler "Mannheim" for the Nordsee Deutsche Hochseefischerei, Wesermünde, she was requisitioned by the Kriegsmarine as "Externsteine". She was launched in 1944, and completed in July of that year. 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. "Externsteine" had the identification number WBS 11. Her complement was nineteen crew plus eleven meteorologists. She was employed as a weather observation ship off Shannon Island on the northeast coast of Greenland 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".