Thus in 1917 the North Sea barrage was not an answer to the popular proposal "to dig the Germans out of their holes like rats." We did not have a mine which could be laid in such deep waters in sufficient numbers to have formed any barrier at all; and even if we had possessed one, the construction of the barrage would have demanded such an enormous number that they could not have been manufactured in time to finish the barrage until late in the year 1918. Presently the situation began to change. The principal fact which made possible this great enterprise was the invention of an entirely new type of mine. The old mine consisted of a huge steel globe, filled with high explosive, which could be fired only by contact. That is, it was necessary for the surface of a ship, such as a submarine, to strike against the surface of the mine, and in this way start the mechanism which ignited the explosive charge. The fact that this immediate contact was essential enormously increased the difficulty of successfully mining waters that range in depth from 400 to 900 feet. If the mines were laid anywhere near the surface, the submarine, merely by diving beneath them, could avoid all danger; if they were laid any considerable depth, it could sail with complete safety above them. Thus, if such a mine were to be used at all, we should have had to plant several layers, one under the other, down to a depth of about 250 feet, so that the submarine, at whatever depth it might be sailing, would be likely to strike one of these obstructions. This required such a large number of mines as to render the whole project impossible. We Americans may take pride in the fact that it was an American who invented an entirely new type of mine and therefore solved this difficulty. In the summer of 1917 Mr. Ralph C. Browne, an electrical engineer of Salem, Mass., offered a submarine gun for the consideration of Commander S. P. Fullinwider, U.S.N., who was then in charge of the mining section of the Bureau of Ordnance. As a submarine gun this invention did not seem to offer many chances of success, but Commander Fullinwider realized that it comprised a firing device of excellent promise. The Bureau of Ordnance, assisted by Mr. Browne, spent the summer and autumn experimenting with this contrivance and perfecting it; the English mining officers who had been sent to America to co-operate with our navy expressed great enthusiasm over it; and some time about the beginning of August, 1917, the Bureau of Ordnance came to the conclusion that it was a demonstrated success. The details of Mr. Browne's invention are too intricate for description in this place, but its main point is comprehensible enough. Its great advantage was that it was not necessary for the submarine to strike the mine in order to produce the desired explosion. The mine could be located at any depth and from it a long "antenna," a thin copper cable, reached up to within a few feet of the surface, where it was supported