The ship was protected by a waterline armored belt that was thick amidships. The conning tower had thick sides, and the deck was covered with thick armor plate. "Brummer" was ordered under the contract name "C" and was laid down at the AG Vulcan shipyard in Stettin in 1915. She was launched on 11 December 1915, after which fitting-out work commenced. Completed in less than four months, she was commissioned into the High Seas Fleet on 2 April 1916. "Brummer" was ready for service with the fleet by May 1916, though she did not steam with the rest of the High Seas Fleet for the Battle of Jutland at the end of the month. In the autumn of 1917, Admiral Reinhard Scheer, the chief of the "Admiralstab", decided to supplement the U-boat campaign with surface raiders to attack the British convoys to Scandinavia. In addition to damaging British shipping, Scheer sought to divert escorts from the Atlantic theater, where his U-boats were concentrated. "Brummer", commanded by "Fregattenkapitän" Leonhardi, and "Bremse", commanded by "Fregattenkapitän" Westerkamp, were selected for the first such operation. Their high speed and large radius of action, coupled with their resemblance to British light cruisers, made them suited to the task. In preparation for the raid, their crews painted the ships dark gray to further camouflage them as British vessels. Half an hour after dawn on the morning of 17 October, "Brummer" and "Bremse" attacked a westbound convoy about east of Lerwick. The convoy consisted of twelve merchantmen and was escorted by the destroyers and and a pair of armed trawlers. The German ruse worked, and the British destroyers initially thought they were friendly ships. They flashed recognition signals until the Germans opened fire at a range of . "Strongbow" was quickly destroyed, and as "Mary Rose" rushed to engage, she too was sunk. The Germans then quickly sank nine of the merchant vessels; the two trawlers and three merchant ships managed to escape. The British Admiralty was not informed of the attack until "Brummer" and "Bremse" were on the return leg of the voyage. Kaiser Wilhelm II celebrated the results of the attack with champagne. The success of the two ships and the commitment of heavier British convoy escorts led Scheer to attempt to attack one of the heavily defended convoys with the entire High Seas Fleet in April 1918, though this ended without success.