Proximity Fuzes

By late 1939, the war in Europe was already several months old and Tuve foresaw the inevitable involvement of the United States. He abandoned experimental work and turned his remarkable talents to the problem of what scientists in the United States should be doing to help remedy the desperately inadequate quality of our military establishment. He made intensive inquiries, especially among high ranking naval officers, and returned to DTM with a vivid impression of the ineffectiveness of antiaircraft guns and with full knowledge of the embryonic British work on proximity fuzes for eliminating the range error of time-fuzed projectiles. He seized on this as the matter to which he would devote his own staff and, by recruitment, other physicists and engineers of kindred inclination -- including Ellett from Iowa and Charles Lauritsen, his son Thomas, and William Fowler from Caltech. As a Carnegie fellow, I was apart from these early efforts but by the summer of 1940, I asked to become a part of this enterprise and was appointed to a staff position in Section T (for Tuve) of the National Defense Research Council (NDRC) of the newly created Office of Scientific Research and Development, headed by Vannevar Bush.

I worked first on a photoelectric proximity fuze and succeeded in solving the basic problem of making a circuit such that the fuze would have equal sensitivity over a large range of ambient light levels. My circuit gave an output approximately proportional to the logarithm of the current from a photoelectric cell by using a fundamental characteristic of a vacuum tube diode. My demonstration of a breadboard of this circuit to Charlie Lauritsen and Willy Fowler showed that I got the same size pulse by waving my hand in front of a photocell when illuminated by full sunlight as I got in a darkened room. Their exuberant response not only made my day, it propelled the photoelectric fuze into the realm of serious consideration.

But soon thereafter, I was transferred to work on the radio proximity fuze. Dick Roberts had built a simple self-excited r.f. oscillator operating at about 70 MHz after the fashion of the one that the British called an autodyne circuit. In brief, the plate current of the one-tube oscillator with a short antenna was affected by the reflected signal from a nearby conductor. The basic scheme was that the transient pulse as a fuze passed an aircraft could be amplified so as to trigger a gaseous tube (thyratron) to fire the detonator of the projectile. This device became the focus of a truly huge development.

For the first time in my life I worked under conditions in which urgency was the motto, multiple approaches to a problem were fostered, money was no object, and the first approximation to a solution was the prime objective. As Tuve put it, "I don't want you to waste your time saving money."