G12 remained the leader of the 5th Torpedo boat flotilla of the German High Seas Fleet on the outbreak of war. On 28 August 1914, the British Harwich Force, supported by light cruisers and battlecruisers of the Grand Fleet, carried out a raid towards Heligoland with the intention of destroying patrolling German torpedo boats. The German defensive patrols around Heligoland consisted of one flotilla (the 1st Torpedo-boat Flotilla) of 12 modern torpedo boats forming an outer patrol line about North and West of Heligoland, with an inner line of older torpedo boats of the 3rd Minesweeping Division at about . The 5th Torpedo-boat flotilla, together with four German light cruisers, waited near Heligoland in support. The 5th Torpedo-boat Flotilla, including G12, were sent out from Heligoland to investigate sightings of British submarines, and ran into several British destroyers. The Flotilla then turned away to try and escape the trap, but the torpedo boat , which along with could not make full speed and lagged behind the rest of the flotilla, was hit by British shells before the arrival of the German cruiser allowed the 5th Flotilla to escape. The torpedo boat of the outer screen did not manage to evade the British force and was sunk. The intervention of the supporting British forces resulted in the sinking of the German cruisers , and . The British light cruiser and destroyers , and were badly damaged but safely returned to base. G12 was undamaged.
