On 30 November 1916, the German commerce raider Wolf, commanded by Fregattenkapitan Karl Nerger, left Kiel. Wolf was a merchant ship that had been armed with 15cm guns, torpedo tubes, over 450 sea mines, and a reconnaissance seaplane. These armaments were hidden, allowing the ship to approach other merchant ships without causing alarm.
For fifteen months Wolf sailed around the horn of Africa, to India, and around Australia and New Zealand, before returning to Germany and a hero’s welcome. During their voyage, they captured or sunk 14 allied ships, and laid mines that sank a further 13. Not once did Wolf need to visit a port, surviving instead off what was captured from the ships they sunk.
On the night of 3-4 July, 1917, Wolf laid 30 mines off Gabo Island in Victoria. Two days later, SS Cumberland struck one of the mines, and was assisted by the Imperial Japanese Navy Cruiser Chikuma, which was patrolling Australian waters. The minefield was cleared by the Royal Australian Navy, with the exception of this mine, which was discovered in 1929.
The mine is an example of a Type II sea mine. It was moored to the sea bottom by an anchor, which detached from the mine after being dropped in the water. It had five ‘Hertz’ or chemical horns, which would bend on contact with a ship, breaking the acid vial inside, which charged the battery and detonated the mine.