According to Archibald Hurd, a British authority on naval matters, the area in the North Sea which was proclaimed by the British Government as dangerous to shipping and therefore prohibited after May 15 is the greatest mine field ever laid for the special purpose of foiling submarines. It embraces 121,782 square miles, the base forming a line between Norway and Scotland, and the peak extending northward into the Arctic Circle. A Secret Chapter of U-Boat History How Ruthless Policy Was Adopted _The causes that led to Germany's adoption of the policy of unrestricted submarine warfare on Feb. 1, 1917, were revealed a year later by the Handelsblad, an Amsterdam newspaper, whose correspondent had secured secret access to "a number of highly interesting and important documents" long enough to read them and make notes of their contents. The Dutch paper vouched for the accuracy of the following information:_ At the close of the year 1915 the German Admiralty Staff prepared a semi-official memorandum to prove that an unrestricted submarine campaign would compel Great Britain to sue for peace "in six months at the most." The character of the argument conveys the impression that the chiefs of the German Admiralty Staff had already made up their minds to adopt the most drastic measures in regard to submarine warfare, but that they wished to convince the Kaiser, the Imperial Chancellor, and the German diplomatists of the certainty of good results on economic and general, rather than merely military, grounds. To this end the memorandum based its arguments on statistics of food prices, freight, and insurance rates in Great Britain. It pointed out that the effects on the prices of essential commodities, on the balance of trade, and, above all, on the morale of the chief enemy, had been such, even with the restricted submarine campaign of 1915, that, if an unrestricted submarine war were decided upon, England could not possibly hold out for more than a short period.