HMS Swordfish
... that the British steam-powered submarine HMS Swordfish's performance underwater was so unsatisfactory that she was converted to an anti-submarine patrol boat in 1917–18?
... that the British steam-powered <a href="./Submarine" id="mwDVA" rel="mw:WikiLink" title="Submarine">submarine</a> <b id="mwDVE"><a about="#mwt37" data-mw='{"parts":[{"template":{"target":{"wt":"HMS","href":"./Template:HMS"},"params":{"1":{"wt":"Swordfish"},"2":{"wt":"1916"},"3":{"wt":"6"}},"i":0}}]}' href="./HMS_Swordfish_(1916)" id="mwDVI" rel="mw:WikiLink" title="HMS Swordfish (1916)" typeof="mw:Transclusion">HMS<span typeof="mw:Entity"> </span><i>Swordfish</i></a></b><span about="#mwt38" class="nowrap" data-mw="{&quot;parts&quot;:[{&quot;template&quot;:{&quot;target&quot;:{&quot;wt&quot;:&quot;'&quot;,&quot;href&quot;:&quot;./Template:'&quot;},&quot;params&quot;:{},&quot;i&quot;:0}}]}" id="mwDVM" style="padding-left:0.1em;" typeof="mw:Transclusion"><span typeof="mw:Entity">'</span></span>s performance underwater was so unsatisfactory that she was converted to an anti-submarine <a href="./Patrol_boat" id="mwDVQ" rel="mw:WikiLink" title="Patrol boat">patrol boat</a> in 1917–18?