▁version ▁of ▁the ▁James ▁W att ▁ 9 1 ▁sc rew ▁two - de cker . ▁ ▁She ▁was ▁a ▁successful ▁experiment . ▁ ▁In ▁service ▁she ▁was ▁very ▁highly ▁regarded . ▁ ▁The ▁Con quer or ▁was ▁designed ▁as ▁a ▁slightly ▁el ong ated ▁St ▁Jean ▁d ' A cre , ▁and ▁was ▁laid ▁down ▁on ▁the ▁same ▁s lip ▁at ▁Dev on port ▁on ▁ 2 5 ▁July ▁ 1 8 5 3 . ▁ ▁Service ▁ ▁St ▁Jean ▁d ' A cre ▁was ▁commission ed ▁at ▁P ly mouth ▁by ▁Captain ▁Henry ▁Ke ppel ▁on ▁ 2 1 ▁May ▁ 1 8 5 3 . ▁ ▁She ▁was ▁completed ▁for ▁sea ▁on ▁ 2 0 ▁September ▁ 1 8 5 3 . ▁She ▁served ▁in ▁the ▁Western ▁Squadron . ▁ ▁Her ▁tri als ▁at ▁Sto kes ▁Bay ▁were ▁on ▁ 3 ▁December ▁ 1 8 5 3 , ▁where ▁she ▁made ▁an ▁average ▁of ▁ 1 1 . 1 9 9 ▁kn ots . ▁ ▁Origin ally ▁it ▁was ▁intended ▁to ▁fit ▁the ▁ 7 0 0 ▁n hp ▁Nap ier ▁engine ▁from ▁the ▁iron - fr ig ate ▁Sim oom , ▁but ▁it ▁was ▁decided ▁that ▁as ▁St ▁Jean ▁d ' A cre ▁was ▁a ▁new ▁ship , ▁they ▁would ▁order ▁a ▁new ▁engine . ▁ ▁She ▁was ▁therefore ▁fitted ▁with ▁a ▁ 6 0 0 ▁n hp ▁P enn ▁two - cy l inder ▁horizontal ▁single - exp ansion ▁tr unk ▁engine . ▁ ▁The ▁cyl ind ers