Problem: how to make a jet engine work under water. Solution: make it use a fuel that burns in water instead of in air.
Dr. Fritz Zwicky, astronomer, physicist and rocket expert of Caltech, has developed such an engine for the U.S. Navy, which presumably hopes to use it in torpedoes or in anti-submarine devices. The Navy is so excited about it that it won't allow Swiss-born Astronomer Zwicky to open his mouth on the subject. It has also warned Aerojet Engineering Corp. of Azusa, Calif., which is working on the device, to keep it quiet.
The waterborne jet works on much the same principle as the airborne ramjet. It consists of a roughly cylindrical chamber with openings at both ends. As the engine moves forward, water comes in the front opening and is mixed with a "water reactive propellant." A "surface tension depressant" (wetting agent) is injected into the water too, presumably to help the fuel mix with the water stream or to help bubbles form.
There are plenty of propellants that burn when brought in contact with water, e.g., metallic potassium, sodium, white phosphorus, various metallic hydrides. Some of these can be used in convenient liquid form. When such fuels hit water, they decompose it violently by uniting with its oxygen, giving off heat and a large volume of hydrogen gas. The combustion chamber is shaped so as to make the expanding water-and-gas mixture shoot out the rear opening as a high-speed jet. The reaction from this drives the engine (and the torpedo) forward.
None of this information has been released by the tight-lipped Navy, but the latest Official Gazette of the U.S. Patent Office (sold to all askers for $17.50 per year) contains a fair description, between an automatic arc starter and a wire cheese slicer, of U.S. Patent 2,461,797, Zwicky's underwater jet.