The devices which have been proposed for capturing and destroying the U-boats in order that navigation upon the Atlantic Ocean may be made safe have run into the thousands. I have had hundreds of impractical schemes sent to me, and the Navy Department and the Naval Consulting Board have been almost swamped by the various suggestions that have been pouring in from all over the country in response to editorials in the newspapers to "Save us from the U-boat!"; "American inventors, rise in your might and strike down this peril which works unseen, like an assassin in the dark!" etc. The devices proposed run all the way from blowing up the whole restricted area or war zone of the ocean to fishing for submarines from aeroplanes, which latter method offers a good chance for sport, at least; and if the submarine designers and commanders were asleep the fishermen might have a good chance of making a catch. Many of my engineering friends with whom I have discussed the U-boat problem have urged upon me that I ought, in order to save the time, energy, and money of many earnest and patriotic--but misinformed--citizens, to publish some material showing the fallacies in many of these schemes which apparently are so promising, and at the same time to point out wherein some have value, and along what lines I believe success to be attainable. At the beginning of the war I myself sent to the Navy Department a number of devices for detecting the presence of and destroying submarines in shoal waters, some of which may have already been known to the Navy Department, and several of which I have since seen published as being the ideas of others; this goes to show that where many minds are working toward the solution of any particular problem several are likely to arrive at the same point. In the interest of public policy I do not think that any device hitherto unknown which offers a chance of success if used against an enemy U-boat should be described, and therefore I should not describe any such device if such were known, but shall limit my remarks to a discussion of some of the devices that have been proposed and described publicly. Trying to serve the country by developing a certain idea, when that idea is itself old or impractical, is evidently a waste of mental energy and money. Further, to show how some of these methods of attack may be offset by the submarine commanders will also serve to prevent the country from relying on false defences; the submarine is a real menace, and should not be lightly regarded. I hope to impress upon people that this is a very serious proposition. It is a problem which should and does attract the leading minds of the mechanical world; and it is not to be coped with by any fanciful notions. While the devices proposed thus far are individually very numerous, they may be classified into a few distinct categories. I would designate them as follows: _Offensive Devices:_