▁of ▁B ona ▁F ides ▁attack er , ▁U B - 4 ▁did ▁approach ▁a ▁group ▁of ▁sm acks ▁in ▁the ▁vic inity ▁the ▁next ▁day , ▁but ▁un be known st ▁to ▁U B - 4 s ▁commander , ▁G ross , ▁one ▁of ▁the ▁fish ing ▁vessels ▁was ▁actually ▁a ▁British ▁de co y ▁ship . ▁ ▁The ▁de co y ▁or ▁Q - ship ▁was ▁His ▁Majesty ' s ▁Ar med ▁Sm ack ▁, ▁a ▁sm ack ▁that ▁had ▁been ▁out f itted ▁with ▁a ▁conce aled ▁ 3 - p ound er ▁( 4 7   mm ) ▁gun . ▁Ar ound ▁ 2 0 : 2 0 , ▁U B - 4 ▁drew ▁within ▁ ▁of ▁In ver ly on ▁and ▁G ross , ▁on ▁the ▁con ning ▁tower ▁of ▁U B - 4 , ▁shout ed ▁out ▁commands ▁to ▁In ver ly ons ▁crew ▁in ▁German . ▁After ▁waiting ▁until ▁the ▁right ▁moment , ▁Ernest ▁Je han , ▁a ▁Royal ▁Navy ▁gun ner ▁in ▁command ▁of ▁In ver ly on , ▁ordered ▁the ▁White ▁En sign ▁raised ▁and ▁gave ▁the ▁command ▁to ▁open ▁fire . ▁A ▁burst ▁of ▁three ▁r ounds ▁from ▁the ▁ 3 - p ound er ▁scored ▁hits ▁on ▁the ▁con ning ▁tower , ▁the ▁second ▁destroy ing ▁part ▁of ▁the ▁bridge ▁and ▁sending ▁G ross ▁into ▁the ▁water . ▁U B - 4 , ▁with ▁no ▁one ▁at ▁the ▁hel m , ▁dr ift ed ▁behind ▁In ver ly on , ▁and ▁when