Could it have been built in 1917, a year earlier than it was? Strauss said it could, and this was the firm belief of Earle and other ordnance experts. True, the antenna mine we developed later was a big improvement, superior to any previously devised. It would have taken two or three times as many mines of the type then in use, perhaps 180,000 of them, as was estimated. We manufactured 100,000 of the antenna type, and could have made as many more, if necessary. The British had no antenna mines, Admiral Strauss pointed out, and all the mines they laid in the barrage were of the older type. After all the objections were presented to him, Admiral Strauss, when asked if he still considered it would have been feasible to have gone ahead with the barrage in 1917, unhesitatingly answered: "Yes." Not laying that barrage earlier--in fact, at the earliest possible moment--was, in my opinion, the greatest naval error of the war. If the British had erected it early in the war, and put a similar effective barrier across the Straits of Dover and Otranto, the Germans would have been so restricted that widespread U-boat warfare, with its terrible destruction of life and shipping, would have been impossible. "Shutting up the hornets in their nests," as President Wilson expressed it, was the first idea that occurred to us when we went to war. The Bureau of Ordnance on April 15, 1917, submitted a memorandum urging that we "stop the submarines at their source" and suggesting that mine barriers be laid across the North Sea, the Adriatic and the Dardanelles. "The northern barrier," it stated, "would extend from the mid-eastern coast of Scotland to the Norwegian coast, a distance of about 250 miles," and the southern (that is, to close the Straits of Dover) would extend "from the southeast coast of England and to a point on the French coast near the Belgian frontier, a distance of about forty miles." Next day I cabled Admiral Sims, who had just arrived in London: Is it not practicable to blockade German coast efficiently and completely, thus making practically impossible the egress and ingress of submarines? The steps attempted or accomplished in this direction are to be reported at once. Two days later came the answer: To absolutely blockade the German and Belgian coast against the entrance and departure of submarines has been found quite unfeasible.