 Complete the following phrase:  On the evening of 12 April 1915, the German airship L7 sighted a British light cruiser and five surfaced submarines in the Heligoland Bight. I Flotilla was ordered out to attack the submarines, but G197, and collided in thick fog, disabling the three ships and causing the sortie to be aborted. In August 1915 the Germans detached a large portion of the High Seas Fleet for operations in the Gulf of Riga in support of the advance of German troops. It was planned to enter the Gulf via the Irben Strait, defeating any Russian naval forces and mining the entrance to Moon Sound. G197 took part in 