Naval mine technology
A naval mine is a container packed with explosives and placed at sea to wait for a ship to pass. The mine is set off when it is disturbed either directly or indirectly by the passing ship.
All the naval mines that were laid in the Skagerrak were moored mines, which was necessary due to the considerable depths of these waters. Moored mines were kept in place by a heavy iron sinker that rested on the floor of the sea. The mines were fastened to their sinkers by a steel cable, which could measure up to 500 metres in length. Mines generally floated 3–6 metres beneath the surface of the water.
Most of the mines laid in the Skagerrak were horned mines. These were set off when the mine’s “horn” was bent in a collision with a passing ship.
In addition, some mines were equipped with contacts that stuck out from the mine like a horn, but that were connected by wires and a battery. When the contact was broken, the mine exploded.
Finally, a number of mines featured a magnetic triggering system. These mines did not detonate as a result of direct contact with a ship, but because of changes in the earth’s natural magnetism that occurred when an iron ship passed over the mine.
In order to prevent minesweeping activities, or at least to make these more difficult, buoys were developed to protect the minefields against sweeping.
Moored mines are cleared by minesweepers, which pull a steel wire behind them or between two ships. This steel wire was designed to cut the mines’ sinker cables on contact.
The purpose of the protective buoys in minefields was to destroy the wires on the minesweepers. These could be destroyed in different ways, such as via explosives or by severing them with a heavy chain or iron knife fastened to the sinker cable.