"Helgoland" was armed with a main battery of twelve SK L/50 guns in six twin gun turrets, with one turret fore, one aft, and two on each flank of the ship. The ship's secondary battery consisted of fourteen SK L/45 guns, all of which were mounted in casemates in the side of the upper deck. For defense against torpedo boats, she carried fourteen SK L/45 guns. After 1914, two of the 8.8 cm guns were removed and replaced by 8.8 cm anti-aircraft guns. "Helgoland" was also armed with six submerged torpedo tubes; one was in the bow, one in the stern, and two on each broadside.