Edison signified his assent, agreeing to give his whole time to the government without charge, and returned to his laboratory. He immediately put everything else aside, and with characteristic enthusiasm and energy delved into the work he had undertaken. The problems referred to covered a wide range of the sciences and arts, and time being an essential element, he added to his laboratory staff by gathering together from various sources a number of young men, experts in various lines, to assist him in his investigations.
Inasmuch as Edison's war work for the government occupied his entire time for upward of two years, it is manifestly out of the question to narrate the details within the limits of a chapter. We must, therefore, be content to itemize the principal problems upon which he occupied himself and assistants and as to which he reported definite results to Washington. The items are as follows:
- Locating position of guns by sound-ranging.
- Detecting submarines by sound from moving vessels.
- Detecting on moving vessels the discharge of torpedoes by submarines.
- Quick turning of ships.
- Strategic plans for saving cargo boats from submarines.
- Collision mats.
- Taking merchant-ships out of mined harbors.
- Oleum cloud shells.
- Camouflaging ships and burning anthracite.
- More power for torpedoes.
- Coast patrol by submarine buoys.
- Destroying periscopes with machine-guns.
- Cartridge for taking soundings.
- Sailing-lights for convoys.
- Smudging sky-line.
- Obstructing torpedoes with nets.
- Under-water search-light.
- High-speed signaling with search-lights.
- Water-penetrating projectile.
- Airplane detection.
- Observing periscopes in silhouette.
- Steamship decoys.
- Zigzagging.
- Reducing rolling of warships.
- Obtaining nitrogen from the air.
- Stability of submerged submarines.
- Hydrogen detector for submarines.
- Induction balance for submarine detection.
- Turbine head for projectile.
- Protecting observers from smoke-stack gas.
- Mining Zeebrugge harbor.
- Blinding submarines and periscopes.
- Mirror-reflection system for warships.
- Device for look-out men.
- Extinguishing fires in coal bunkers.
- Telephone system on ships.
- Extension ladder for spotting-top.
- Preserving submarine and other guns from rust.
- Freeing range-finder from spray.
- Smudging periscopes.
- Night glass.
- Re-acting shell.
It will be seen that Mr. Edison's inventive imagination was permitted a wide scope. He fairly reveled in the opportunity of attacking so many difficult problems and worked through the days and nights writh unflagging enthusiasm. He committed his business interests to the care of his associates, and during the two years of his work for the government kept in touch with his great business interests only by means of reports which were condensed to the utmost. In addition, for two successive winters, he gave up his regular winter vacation on his Florida estate, usually a source of great enjoyment to him. But it was all done willingly and without a word of regret or dissatisfaction so far as the writer's knowledge goes.
Although we cannot take space to discuss the above items in detail, the reader will probably have a desire to know something of Edison's work in regard to the submarines.
In view of the vast destruction of shipping, perhaps it is not an overstatement to say that the most vital problem of the late war was to overcome the menace of the submarine. Undoubtedly there was more universal study and experiment on means and devices for locating and destroying submarines than on any other single problem.
The class of apparatus most favored by investigators comprised various forms of listening devices by means of which it was hoped to detect and locate by sound the movement of an entirely submerged submarine. The difficulties in obtaining accurate results were very great even when the observing vessel was motionless, but were enormously enhanced on using listening devices on a vessel under way, on account of the noises of the vessel itself, the rushing of the water, and so on.
Edison's earliest efforts were confined to the induction balance, but after two months of intensive experimenting on that line he gave it up and entered upon a long series of experiments with listening devices, employing telephones, audions, towing devices, resonators, etc. The Secretary of the Navy provided Edison with a 200-foot vessel for his experiments, and in the summer and fall of 1917 they had progressed sufficiently to enable him to detect sounds of moving vessels as far distant as five thousand yards. This, however, was when the observing vessel was at anchor. The results with the vessel under way, at full speed, were not poor.
Having pushed the possibilities along this line to their reasonable limit, Edison was of the opinion that this plan would not be practical and he turned his thoughts to another solution of the problem—namely, to circumvent the destructive operation of the submarine and avoid the loss of ships. He had discovered in his experimenting that the noise made by a torpedo in its swift passage through the water was very marked and easily distinguishable from any other sound.
With this fact as a basis, Edison, therefore, evolved a new plan, which had two parts: first, to provide merchant-ships with a listening apparatus that would enable them, while going at full speed, to hear the sound of a torpedo as soon as it was launched from a submarine; and, second, to provide the merchant-ships with means for quickly changing their course to another course at right angles. Thus, the torpedo would miss its mark and the merchantship would be saved. If another torpedo should be launched, the same tactics could be repeated.