Rollmann joined the Reichsmarine of the Weimar Republic on 1 April 1926 as a member of "Crew 26" (the incoming class of 1926).

In seven successful combat patrols, he sank 19 merchant ships (including the neutral, clearly marked and fully lit, Greek merchantman Eleni Stathatou and the neutral Petsamo of Finland, with a cargo of maize, sailing from neutral Rosario to neutral Cork), as well as the British destroyer HMS Whirlwind, the submarine HMS Spearfish,[2] and the Norwegian minelayer HNoMS Frøya.

[3] On all seven patrols Leutnant zur See Hans-Hartwig Trojer served as second watch officer on U-34.

In February 1943 he commissioned the Type IXD U-boat U-848, sinking one merchant ship on his first and only patrol, bringing his career total to 20 merchant ships sunk for a total of 96,562 GRT, three warships sunk (2,365 GRT) and two ships captured for a total of 4,957 GRT.

[6] Wilhelm Rollmann and his entire crew were killed in action on 5 November 1943 when U-848 was sunk by depth charges from three Liberator and two Mitchell aircraft from the United States Navy Squadron VB-107 and the US Army 1st Composite Squadron south-west of Ascension Island.