inder ▁having ▁its ▁own ▁inject or ▁and ▁p ump , ▁driven ▁by ▁its ▁own ▁cam ▁lo be . ▁ ▁Us es ▁ ▁Naval ▁service ▁▁ ▁Development ▁began ▁in ▁ 1 9 4 7 ▁and ▁the ▁first ▁D elt ic ▁model ▁was ▁the ▁D 1 8 - 1 1 B , ▁produced ▁in ▁ 1 9 5 0 . ▁It ▁was ▁designed ▁to ▁produce ▁ ▁at ▁ 2 0 0 0 ▁r pm ▁for ▁a ▁ 1 5 - min ute ▁rating ; ▁the ▁continuous ▁rating ▁being ▁ ▁at ▁ 1 7 0 0 ▁r pm , ▁based ▁on ▁a ▁ 1 0 0 0 - hour ▁over ha ul ▁or ▁replacement ▁life . ▁By ▁January ▁ 1 9 5 2 ▁six ▁engines ▁were ▁available , ▁enough ▁for ▁full ▁development ▁and ▁end urance ▁tri als . ▁A ▁captured ▁German ▁E - Bo at ▁S 2 1 2 ▁was ▁selected ▁as ▁it ▁was ▁power ed ▁by ▁Mer cedes - B enz ▁dies els ▁with ▁approximately ▁the ▁same ▁power ▁as ▁the ▁ 1 8 - cy l inder ▁D elt ics . ▁When ▁two ▁of ▁the ▁three ▁Mer cedes - B enz ▁engines ▁were ▁replaced , ▁the ▁compact ness ▁of ▁the ▁Nap ier ▁engines ▁was ▁graph ically ▁illustrated — they ▁were ▁half ▁the ▁size ▁of ▁the ▁original ▁engines ▁and ▁approximately ▁one ▁fifth ▁the ▁weight . ▁ ▁Pro ving ▁successful , ▁D elt ic ▁Dies el ▁engines ▁became ▁a ▁common ▁power ▁plant ▁in ▁small ▁and ▁fast ▁naval ▁craft . ▁The ▁Royal ▁Navy ▁used ▁them ▁first ▁in ▁the