▁Dark ▁class ▁fast ▁attack ▁craft . ▁Sub sequently ▁they ▁were ▁used ▁in ▁a ▁number ▁of ▁other ▁smaller ▁attack ▁craft . ▁Being ▁largely ▁of ▁al umin ium ▁construction , ▁their ▁low ▁magnetic ▁signature ▁allowed ▁their ▁use ▁in ▁mine ▁counter me asures ▁vessels ▁and ▁the ▁D elt ic ▁was ▁selected ▁to ▁power ▁the ▁Ton ▁class ▁mines we eper . ▁The ▁D elt ic ▁engine ▁is ▁still ▁in ▁service ▁in ▁the ▁H unt ▁class . ▁These ▁versions ▁are ▁de - r ated ▁to ▁reduce ▁engine ▁stress . ▁ ▁D elt ic ▁Dies els ▁served ▁in ▁M TB s ▁and ▁P T ▁boats ▁built ▁for ▁other ▁nav ies . ▁Part icular ly ▁notable ▁was ▁the ▁Norwegian ▁T j eld ▁or ▁N ast y ▁class , ▁which ▁was ▁also ▁sold ▁to ▁Germany , ▁Greece , ▁and ▁the ▁United ▁States ▁Navy . ▁N ast y ▁class ▁boats ▁served ▁in ▁the ▁Vietnam ▁War , ▁largely ▁for ▁cover t ▁operations . ▁ ▁Sm aller ▁nine - cy l inder ▁D elt ic ▁ 9 ▁engines ▁were ▁used ▁as ▁marine ▁engines , ▁not ably ▁by ▁mines we ep ers . ▁The ▁Ton ▁class ▁vessels ▁were ▁power ed ▁by ▁a ▁pair ▁of ▁D elt ic ▁ 1 8 s ▁and ▁used ▁an ▁additional ▁D elt ic ▁ 9 ▁for ▁power ▁generation ▁for ▁their ▁magnetic ▁influence ▁swe ep . ▁The ▁H unt ▁class ▁used ▁three ▁D elt ic ▁ 9 s , ▁two ▁for ▁prop ulsion ▁and ▁again ▁one ▁for ▁power ▁generation , ▁but ▁this ▁time ▁with ▁a ▁hyd ra ul ic ▁p ump