The confusion is that the building fronts on two streets, it is No 9 on Blvd M and No 18 on Blvd Suchet. It is a big building (See Paris street map) Donitz had his living quarters on the second floor others were for U-boat operations. I think it was used for all U-boat operations a few months after Sept 1942. If you live in the EU just hop a train to Paris to see it. Will take a short time to see from whereever you are in the EU. Also see Hotel Majestic (gestapo) HQ and museum during the war and Hotel Maurice army HQ. Salle Wagram is worth a visit too where the anti Red pro Axis rallies were held during the war. The city has lots of WWII sites and are close to train stations. The pent house added to roof had at least 50 antennas on the roof when I saw it a few years ago.