The process of shipping the submarines by rail involved breaking the submarines down into what was essentially a knock down kit . Each boat was broken into approximately fifteen pieces and loaded on to eight railway flatcars . Type UB I boats destined for service with the Flanders Flotilla made a five @-@ day journey to Antwerp for the two- to three @-@ week assembly process . After assembly at Antwerp the boats were towed by barge to Bruges for trials . Boats selected for service in the Mediterranean were sent to the Austro @-@ Hungarian port of Pola for assembly . The total time from departure of the railcars from the shipyard to operational readiness for the boats was about six weeks .