5th U-boat Flotilla - Training flotilla in Kiel 18th U-boat Flotilla - Training flotilla in Poland which performed combat operations in the Baltic Sea 19th U-boat Flotilla - Training flotilla in Kiel for prospective U-boat commanders 20th U-boat Flotilla - Training flotilla in the Baltic (Baltiysk) 21st U-boat Flotilla - Primary "basic training" flotilla for the U-boat service 22nd U-boat Flotilla - Training flotilla in Wilhelmshaven 24th U-boat Flotilla - Training flotilla in Danzig 25th U-boat Flotilla - Naval artillery training flotilla in Danzig 26th U-boat Flotilla - The U-boat service's torpedo training school 27th U-boat Flotilla - U-boat tactical operations training school