German navy increasing number of submarines according to the Dutch magazine Marineblad dated 1912-1913 no. 5

An item reported that in the spring the German navy intended to commission a second submarine flotilla and the navy would have then 24 submarines. The building of a third flotilla was still going on while a fourth one was being designed. The personnel strength would number 516 men excluded the officers but included 182 deck and 335 engine room personnel. The submarine school was using a full size model inside complete fitted out as a real submarine for training. With the Vulcan were continuously trainings in searching and salvaging sunk submarines.