SM U-6 was one of the 329 submarines serving in the Imperial German Navy in World War I. U-6 was engaged in naval warfare and took part in the First Battle of the Atlantic.

She reached Cap Gris Nez on 27 February, and on 28 February was preparing to carry out an attack on the British steamer Thordis off Beachy Head, when the submarine's periscope was spotted by the merchant ship, which rammed U-6, damaging U-6's periscope.

On 21 July she took two Swedish steamers as prizes and set two more sailing ships (757 tons) carrying timber to Britain on fire.

When she ran low on fuel, U-6 returned to base on 29 July reaching Heligoland the next day.

Beyer, officer of the watch at the time of her sinking, the smoke from U-6's paraffin engines made the commander of the Royal Navy submarine aware of her presence and enabled him to get into launching position.