▁turning ▁circle . ▁Clear ly ▁seen ▁as ▁the ▁linear ▁descend ants ▁of ▁the ▁late ▁ 1 9 th ▁century ▁steam ▁tor ped o ▁boats ▁and ▁coast al ▁destroy ers , ▁many ▁were ▁actually ▁fitted ▁with ▁the ▁ 1 4 ▁in ▁tor ped o ▁tub es ▁removed ▁from ▁old ▁tor ped o ▁boats . ▁ ▁With ▁the ▁surv ival ▁of ▁a ▁builder ' s ▁di ary ▁by ▁William ▁Bart ram , ▁full ▁details ▁of ▁the ▁sea ▁tri als ▁of ▁P . 2 3 ▁on ▁ 2 1 ▁June ▁ 1 9 1 6 ▁exist . ▁She ▁worked ▁up ▁to ▁. ▁Bart ram ' s ▁commission ed ▁a ▁model ▁from ▁S under land ▁model ▁mak er ▁C ▁C raw ford ▁& ▁S ons ▁and ▁this ▁model , ▁in ▁the ▁collections ▁of ▁S under land ▁Museum ▁and ▁Heritage ▁Service , ▁is ▁stored ▁in ▁the ▁model ▁store ▁of ▁Ty ne ▁& ▁W ear ▁Archives ▁& ▁Museum s ▁Service ▁at ▁the ▁Disc overy ▁Museum . ▁ ▁PC ▁class ▁slo ops ▁ ▁Ten ▁of ▁these ▁ships ▁were ▁completed ▁as ▁Q - ships , ▁with ▁their ▁numbers ▁being ▁alter ed ▁by ▁the ▁addition ▁of ▁a ▁" C " ▁after ▁the ▁" P ". ▁These ▁were ▁term ed ▁the ▁PC ▁class ▁slo ops . ▁A ▁further ▁batch ▁of ▁ten ▁ships ▁were ▁ordered ▁in ▁ 1 9 1 7 ▁( PC . 6 5 ▁to ▁PC . 7 0 ▁in ▁January , ▁and ▁PC . 7 1 ▁to ▁PC . 7 4 ▁in ▁June ) ▁as ▁PC ▁class ▁slo ops . ▁These