 The first Type <unk> I to enter service was <unk> @-@ 10 , which formed the nucleus of the Flanders Flotilla , on 27 March 1915 . By the end of April five more Type <unk> I boats had become operational . <unk> @-@ 10 was eventually joined in the Flanders Flotilla by <unk> @-@ 2 , <unk> @-@ 4 , <unk> @-@ 5 , <unk> @-@ 6 , <unk> @-@ 12 , <unk> @-@ 13 , <unk> @-@ 16 , and <unk> @-@ 17 ; of these , only <unk> @-@ 2 made the journey to Flanders by sea rather than rail . 
