MINING THE NORTH SEA.

Manawatu Herald, Volume XXXVI, Issue 1336, 15 December 1914, Page 4

MINING THE NORTH SEA.

DEFENCE AGAINST SUBMARINES

BRITAIN’S REPLY TO GERMANY

(By FRED. T. JANE, in “Land and Water.”)

Tlic Admiralty notification that mines have been laid in a. certain area in the North sea is the immediate answer to the submarining of the three Cressys. The mine field will considerably hamper future German submarine movements, especially those of such submarines as may happen to bo out, and which will know nothing of the danger awaiting their return ,unless warned by those, “observation stations” which the Gormans are supposed to have established on our east coasts.

The weak point of a mine field is that “roads through it” must necessarily exist, and these can, of course, be observed, either directly as our submarines observed them inside the Bight of Heligoland, or by the misuse of neutral fishing craft. On this account alone the closing of all British harbours on the east coast to alien fishing craft, or craft so registered, is a very wise measure, while the public notification of the mine field will'render pretty clear the status of any fishing craft found prowling, about the prohibited area, no matter what flag it may chance to lie flying. German submarines can still emerge from the Heligoland direction, but they will have to come along a more or less well-defined route, where there is just enough vagueness in the Admiralty statement to leave it not (pule clear whether other mined areas than those mentioned do not exist.

Out of all this wc can take it that, so far as the British navy is concerned. the mine is taken to he the answer (or one of the answers) to the submarine. A submarine travelling on the surface has 1 a fair chance of crossing a mine field without much risk, hut a submarine on the surface is no particular danger to anyone. She is easily to he annihilated by destroyers and torpedo boats if detected, and detection is not very diliicnlt. TEN-DAY CRUISES.

ill <*muection with this matter at ten* tion may be drawn to the. circumstance that German, official reports of (submarine movements have frequently referred to “ton-day cruises.” Now, by simple arithmetic we. can easily calculate, that there are few il' any German submarines capable of tenday cruises unaided, allow as we will for lying by on the surface at night. The- utmost radius of anything up to 1124 is, “on paper,” 2000 miles on the. surface. Supposing surface cruising tor only twelve hours out of the twentyfour, this works out about eight days at ton knots, without taking into account fuel expended' in recharging accumulators for under-water work. Of course it is possible for a boat to lie below water with no machinery working, and so far as machinery and fuel supply arc concerned to carry this on fairly ’ indefinitely, so long as she can keep on renewing at intervals her air supply. Nothing very definite is known as to what the fresh air supply method in German boats consists of, hut in any case it is not a. matter to ho arranged tor in a few minutes Apart from this machinery question there is the human element to eon-