 The target was SMS Königin Luise , a former Hamburg @-@ Heligoland excursion boat that had been converted to an auxiliary minelayer by the Germans . They had planned to mount a pair of 8 @.@ 8 @-@ centimetre ( 3 @.@ 5 in ) guns on board , but they did not have the time to do so ; her only armament was a pair of lighter guns and 180 mines . On the night of 4 August , she had departed Emden and headed into the North Sea to lay mines off the Thames Estuary , which she began at to do at dawn . 
