Sub (1-4)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sub</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for u-boat that I've seen before include "German submarine of WW2" , "Take pool exercise" , "Submersible warship armed with torpedoes" , "German WW 2 sub" , "German wartime submarine" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sub</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for alternate that I've seen before include "In turns, first one then the other" , "Interchange" , "Happen in turns, rotate" , "Change repeatedly between two" , "Happening or following in turns, one after the other" .)
(Other definitions for step in that I've seen before include "Substitute" , "enter" , "Shoe with no fastenings" , "Type of garment" , "Intervene dramatically, or at a senior level" .)