In these and other ways over 3000 mines were laid off the British coast in one year. There were also several raids by surface mine-layers, which succeeded in eluding the network of patrols in the fogs and snows which prevail in the North Sea during several months out of every twelve. The two most important of these were the cruises of the _Wolfe_ and the _Moewe_. The former vessel left Germany during the November fogs of 1916, and, by skirting the Norwegian coast, succeeded in passing the British patrol flotillas. She carried 500 mines, and after crossing the North Sea in high latitudes, proceeded down the mid-Atlantic until off the Cape of Good Hope, where the first mine-field was laid. She then crossed the Indian Ocean, laying fields off Bombay and Colombo. It was in these seas that she succeeded in capturing a British merchantman. Placing a German crew and a cargo of mines aboard, she sent the prize to lay a field off Aden, while she herself proceeded to New Zealand. In these far-distant waters another field was laid, and a few months later the last of her cargo was discharged off Singapore. From this time onward she became a commerce raider. [Illustration: FIG. 23.--A typical German mine and sinker. _A._ The mine-casing containing about 300 lb. of high explosive, and the electric firing device which is put in force when the horns _B_ are struck and bent by a passing ship. _B._ Horns, made of lead and easily bent if touched by a surface ship, but sufficiently rigid to resist blows by sea-water. _C._ Hydrostatic device, operated by the pressure of the water at a given depth, rendering the mine safe until submerged. _D._ Slings holding mine to mooring rope _F_. _F._ Mooring rope to reel in sinker. _G._ Reel of mooring wire, which unwinds when the mine floats to the surface. _H._ Iron supports held together (as in small left-hand diagram) by a band round the mine-casing. The mine goes overboard and sinks like this to the bottom. The band is then released by a special device, and the supports drop away, leaving the mine free to float to the surface (as in small right-hand diagram). _I._ A heavy iron sinker which acts as an anchor, holding the mine in one position.] The _Moewe_ left Germany in December, 1916, and crossed the North Sea amid heavy snow squalls. Proceeding into the North Atlantic, she awaited a favourable opportunity to approach the British coast. This came one wild January night with a rising gale and a haze of snow. All her mines, about 400 in number, were laid off the Scottish coast in the teeth of a nor'wester. Then, with the "jolly Roger at the fore," she steamed out on to the wastes of sea lying between the New World and the Old.