 After the German Army 's rapid advance along the North Sea coast in the earliest stages of World War I , the German Imperial Navy found itself without suitable submarines that could be operated in the narrow and shallow seas off Flanders . Project 34 , a design effort begun in mid @-@ August 1914 , produced the Type UB I design : a small submarine that could be shipped by rail to a port of operations and quickly assembled . Constrained by railroad size limitations , the UB I design called for a boat about 28 metres ( 92 ft ) long and displacing about 125 tonnes ( 123 long tons ) with two torpedo tubes . UB @-@ 7 was part of the initial allotment of eight submarines — numbered UB @-@ 1 to UB @-@ 8 — ordered on 15 October from Germaniawerft of Kiel , just shy of two months after planning for the class began . 
