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The 18th U-boat Flotilla (German 18. Unterseebootsflottille) was a short-lived unit of the German Kriegsmarine during World War II.
The flotilla was formed in Hel, Poland, in January 1945 under the command of Korvettenkapitän Rudolf Franzius. Officially a Training Flotilla (Ger. Ausbildungsflottille), the four U-boats were actually in combat in the Baltic Sea. It was disbanded in March 1945.
Assigned U-boats 
Four U-boats were assigned to this flotilla during its service.