TOC | Previous Section: Chapter XL | Next Section: Chapter XLII
History of Communications-Electronics in the United States Navy, Captain Linwood S. Howeth, USN (Retired), 1963, pages 495-500:
The Proximity Fuze
1. THE NAVAL FIRE-CONTROL PROBLEM
The control of projectiles fired from a moving and unsteady platform is one of the most difficult procedures of warfare. The difficulties increase rapidly with range and motion of target and are still further increased when a very small high-speed target is capable of motion in both vertical and horizontal planes and can make radical course and speed changes. The problem must be solved instantaneously and produce absolutely correct course, speed, range, bearing, and position angle, otherwise the predicted point of contact of projectiles and target will be in error and the target will continue undamaged. A duck hunter instinctively takes these variables into account when he takes a lead on his fowl, but he does not have to determine the instant of exploding his charge for that is done at the time of firing, and his charge goes out covering a space that increases rapidly until its range is reached. In long-range firing against aircraft this variable, the time of flight of the projectile until it reaches the proper position in relation to the target, must be considered. At the instant it reaches this position the fuze must detonate the projectile.
With a visible target on a steady course at constant speed, the bearing and position angle can be continually supplied the fire-control equipment electrically. Prior to World War II and the concurrent development of radar, an approximation of range was made by optical equipment and supplied manually to the fire-control equipment. With these three variables the fire-control equipment could determine course and speed and predict future position. However, there was the required estimation of fuze setting, any error in which created a corresponding error in burst. The development of fire-control radar increased range accuracy and allowed it to be fed electrically to the fire-control equipment. There were still inaccuracies in fuze settings which increased with the shorter and shorter solution periods brought about by increased target speeds. Even with extremely accurate bearing, position angle, and range being provided the fire-control equipment to permit it to generate predicted position and to provide gun-laying data, the errors in fuze settings necessitated saturation firing. This was not too effective a defense and its effectiveness decreased more than proportionally with the number of different directions in which the attacking planes came in.
The requirement for a fuze which would detonate a projectile when its target was within its burst range (approximately 70 yards for a 5-inch projectile) was obvious, the means of accomplishing this were not. The ultimate solution is a tribute to the Navy, American scientists, and the American electronics industry.
2. EARLY ATTEMPTS TO DEVELOP A PROXIMITY FUZE1
For a decade prior to World War II, the Navy's Bureau of Ordnance had considered the possibility of developing an infrared fuze which could be triggered by the heat developed by an aircraft engine. The complicated engineering problems involved had proven too great an obstacle to its development.
In the summer of 1940 improved capabilities of aircraft and the precarious international situation necessitated exploration of the entire scientific field, with the highest priority, to the end that a fuze be developed which would detonate a projectile when in proximity of an aircraft. During July meetings a group, constituted of members of the National Defense Research Committee and the Navy Department Council for Research, decided that the development of such a fuze was possible by utilizing either electronic or photoelectric devices. There were no stipulations as to the techniques to be investigated. One month later, the Bureau of Ordnance gave influence fuzes top priority over all projects that it had requested the National Defense Research Committee to investigate.
Later in that month, it was learned that two of our largest electronics manufacturers were providing the British with thousands of vacuum tubes and photoelectric cells. This lead to the belief that they were being used for some type of proximity fuze. Following the arrival, in September 1940, of the British Technical Mission, headed by Sir Henry Tizord, this suspicion was confirmed by a presentation of a summary of their unsatisfactory progress in that field.
During August 1940, Section T of the National Defense Research Committee was established under Dr. M. A. Tuve of the Carnegie Institution. Arrangements were made for the research to be conducted at the laboratory of the Department of Terrestrial Magnetism of the Carnegie Institution, Washington. In November 1940, the Bureau of Standards joined section T on the project and for a few months both of these activities conducted independent research, each working on a variety of devices applicable to a wide range of projectiles. Since the Navy's basic and urgent requirement was for a fuze for antiaircraft projectiles, fired from rifled guns, the work of the two activities was separated in July 1941. Thereafter, Section T devoted its entire energies to this problem, while the Bureau of Standards concentrated on influence fuzes for nonrotating projectiles.
In November 1941, the Bureau of Ordnance contracted with the Crosley Corp. to conduct independent research in fuze construction under the technical supervision of the National Defense Research Committee. This industrial concern was expected to provide realistic engineering design rather than development. Meanwhile, the National Defense Research Committee had made and was continuing to make contracts with numerous companies and universities. The pace of development was so rapid that it exceeded all available research facilities.
The growth of the project was so great that it required increased administrative support. Accordingly, in March 1942, it was placed directly under the Office of Scientific Research and Development, which contracted with Johns Hopkins University to provide for its administration. The secret classification of the project necessitated the provision of secure space for this. The University established the Applied Physics Laboratory at Silver Spring, Md., a suburb of Washington. This Laboratory quickly became the focal point of the project.
During the early months acoustic, thermal, electrostatic, and magnetic types were studied and then abandoned as unsatisfactory. Considerable emphasis was placed on the utilization of photoelectric cells and one was practically completed in early 1941, but the cells failed to withstand the centrifugal force developed by the rotating projectile. Moreover, such a fuze was unsatisfactory since it required daylight for operation.
3. THE DEVELOPMENT OF THE PROXIMITY FUZE2
In early 1941, all contractors supported by Navy funds were directed to concentrate on the development of an electronic fuze. Several means were immediately studied. Among these was one in which the transmission of radio waves from the ground would be reflected by the target and received by and activate the fuze. Another, more logical and the ultimately accepted approach, was to develop a fuze which was capable of obtaining its own intelligence and of using it to ignite the demolition train. In completed form, this fuze would consist of four principal components: A minute radio transceiver, complete with amplifier and capacitor; a battery; an explosive train; and the necessary safety devices. The theory was that the fuze transmitter, alone, would not produce sufficient signal intensity to trigger a thyratron tube switch. However, as the projectile approached a target the radio waves reflected by the target would gradually increase and come more and more into phase with the fuze-generated signal until by the time it was within the fragmentation pattern the intensity of the combined waves would trigger the thyratron tube switch. This would, in turn, release the energy in a charged condenser which would ignite the explosive train. Schematically, it had the appearance of a Rube Goldberg creation. Actually, it was a brilliant conception. To convert it to a workable device required the development of radio components rugged enough to withstand an accelerative force 20,000 times stronger than gravity and a centrifugal force set up by approximately 500 rotations per second, yet small enough, together with the other three components, to be contained in a space approximately the size of a pint milk bottle.
Had the requirement for miniature components of the required ruggedness been submitted to any electronic equipment manufacturer during peacetime he would have most probably shaken his head and declared them far beyond the engineering capabilities of his staff. However, the increased defense such a fuze would provide our ships and cities was sufficient to cause them to make the endeavor. Miniaturization had already had a start in the manufacture of electronic hearing aids but ruggedness was not an essential requirement of that field.
During the development period, the tubes were handmade by engineers of the Western Electric, Raytheon, Hytron, Erwood, and Parker-Majestic Cos. As might be expected, quality varied but intermittent tests conducted throughout the latter half of 1941 offered promise. Wherever weakness was found it was corrected by redesign and strengthening until eventually satisfactory handmade products which were capable of tooled mass production became available.
On 29 January 1942 a group of fuzes with miniaturized components and dry cell batteries, assembled on a pilot line, were installed in standard 5-inch antiaircraft projectiles and fired from a 5-inch 38-caliber antiaircraft gun. At the end of a 5-mile trajectory 52 percent successfully activated themselves by proximity to water. This might appear to be a low percentage but this offered protection far greater than that afforded by saturation firing. The Bureau directed the Crosley Corp. to commence pilot production of the fuzes without delay. At this time it was given the designation VT (variable time).
During the drawing-board stage of the fuze, it had been considered that a small dry cell battery would provide a satisfactory source of energy. During the development period it was found that these batteries often failed to withstand the shock of gunfire and, moreover, were of short life under shipboard storage conditions. Especially in the South Pacific, continued use of this type would require their constant replacement and would cast doubts as to the reliability of the fuze. Parallel research to develop improved dry cells and a wet battery, wherein the electrolyte would be kept separated from the electrode until after the projectile was fired, was concentrated at the Cleveland, Ohio, plant of the National Carbon Co. The latter type proved feasible and was developed into a cylindrical battery, resembling a fountain pen, wherein the electrolyte is contained in a glass ampule at the center of a cylindrical cell of thin plates. Upon the firing of the projectile the shock breaks the ampule, the electrolyte is released and the centrifugal force generated by the rotation of the projectile forces the liquid between the plates and activates the battery. This battery was ready for experimental testing in February 1942.
Development of the fuze continued concurrently with the pilot production at the Crosley Corp. plant. In April 1942, firing tests, in which the new battery was utilized, were conducted successfully, using a small plane suspended from a barrage balloon as a target. Following this, extensive work was conducted to adapt the necessary safety and self-destruction devices to the fuze. After conducting another test, similar to the one conducted on 29 January, 70 percent of the fuzes detonated, and a decision was reached to conduct a shipboard firing test.
4. SERVICE TEST OF THE VT FUZE3
On 12 August 1942, the first precombat service tests were made by the newly commissioned U.S.S. Cleveland, Capt. S. E. Burroughs, USN, commanding, then shaking down in the Chesapeake Bay. Radio-controlled planes (drones) were used as targets. The Gunnery Officer, Lt. Comdr. Russell Smith, USN, was an experienced fire-control officer. His guncrews consisted of approximately 10-percent experienced personnel with the remainder being newly enlisted, who were serving on their first ship. Smith, with his nucleus of experienced personnel, worked assiduously before and during the shakedown period to train his fire control and guncrews and achieved magnificent results. The tests were scheduled for a period of 2 days and were to be conducted under simulated battle conditions. All three available drones were destroyed early on the first day, while their controllers were putting them through all possible evasive maneuvers, by the bursts of four proximity fuzed projectiles. This was an astounding and pleasant sight to all who witnessed it and it was especially so to those who had served in the task force which had made the strikes against the Marshalls, Wake, and Marcus in the early months of 1942, and were aware of the impotency of our antiaircraft defense. Here was a device which would force enemy aviators to be more respectful of distances or else activate our fuzes to accomplish their own destruction.
5. EARLY PRODUCTION UNDER FLUID SPECIFICATIONS4
Following the Cleveland tests fluid specifications, which permitted incorporation of later developments, were drawn up for mass production of the fuze and manufacture was commenced. Those produced were shipped to the Ammunition Depot, Mare Island, Calif., for assembly into antiaircraft projectiles. Samples of these were flown back daily to the U.S. Naval Proving Ground, Dahlgren, Va., for verification of quality.
6. INITIAL COMBAT USE5
When, in the middle of November 1942, 5,000 rounds of proximity-fuzed projectiles were in storage at Mare Island, they were rushed to Noumea for distribution to ships of a task force in the southwest Pacific. The first ship to introduce them to the enemy was the U.S.S. Helena. On 5 January 1943, four Japanese bombers attacked the task force and the Helena downed one with the second salvo of proximity-fuzed ammunition.
7. SECURITY RESTRICTIONS ON USAGE6
Realizing the necessity of keeping the details of the fuze from the enemy, the Combined Chiefs of Staff issued a ban against its use in any locale where a dud or live ammunition might be recovered by the enemy. This restricted its usage to naval warfare and also prevented it from being used in naval bombardment of enemy-held territories.
8. FULL-SCALE PRODUCTION7
Following the Crosley Corp. contract, production was increased with great rapidity. Beginning in September 1942, newly established facilities commenced producing the rugged miniature tube in large quantities. In October 1942 an average of 500 tubes were being manufactured daily. After the fuze had been proven in combat the expansion of manufacturing facilities was rapidly increased. By the end of 1943 almost 2 million had been delivered. By the end of 1944, 87 contractors, operating 10 plants, were manufacturing parts of the fuze which at that time were being delivered at the rate of 40,000 per day. Procurement contracts increased annually from $60 million in 1942, to $200 million in 1943, to $300 million in 1944 and were topped by $450 million in 1945. The increased volume and improved production techniques lowered the cost per fuze from $732 in 1942 to $18 in 1945. This permitted the purchase of over 22 million fuzes for approximately $1,010 million.
Fuze assembly was concentrated in the plants of the Crosley Corp., the Radio Corp. of America, the Eastman Kodak, and the McQuay-Norris Cos. Mass-tube production finally had to be limited to Sylvania Electric Products, Inc., since they proved to be the only firm capable of combining quality and quantity. Cost of tubes declined with increased production from $5.05 in 1942 to $0.40 in 1945.
9. COMBAT USAGE DURING 19438
During 1943 approximately 9,100 rounds of proximity-fuzed and 27,200 rounds of time-fuzed 5-inch antiaircraft projectiles were fired. Fifty-one percent of the hits on enemy planes were credited to VT-fuzed projectiles. Its success in repelling air attacks against fleet units reached its peak when a task group in the Pacific reported the destruction of 91 of 130 attacking Japanese planes. It was being used with like effect against the enemy in the Mediterranean and Atlantic theaters.
10. REMOVAL OF SECURITY RESTRICTIONS AND COMBAT USAGE DURING 19449
During 1944 happenings of dire nature in the European theater of operations necessitated the lifting of the ban against the use of the fuze where it might be recovered by an enemy. On 12 June 1944 the first "buzz bomb" fell on London and it was followed by steadily increasing numbers. The all-out valiant effort of the Royal Air Force failed to cope with the new weapon. The Combined Chiefs of Staff reluctantly agreed upon the necessity of using the proximity fuze in the defense of London. Large numbers of antiaircraft guns were moved to the channel coast where they could fire at the bombs over water. Success in destroying the bombs by gunfire in creased proportionally with the increase in the use of VT-fuzed projectiles. In the last month of the terrifying 80 days, 79 percent of the bombs engaged were destroyed as compared with the 24 percent destroyed during the first week of the attacks. On the last day of large-scale attacks only 4 of 104 bombs succeeded in reaching their target. Some of the 100 destroyed are credited to the Royal Air Force and to the barrage balloons but the majority were victims of proximity-fuzed projectiles. There was little profit to the enemy with such a minute percentage of success so he turned the weapon on the port of Antwerp which at that time was vital to the Allied supply lines. In the autumn of 1944 the devastating damage wrought while the Allies were redeploying antiaircraft guns threatened to close the port. As the number of guns firing the proximity fuze increased, the damage decreased and the Allies were able to move their guns closer and to assume the offensive against the aerial targets. The defense of Antwerp resulted in the Combined Chiefs of Staff removing all bans against the use of the fuze and this was most fortunate. In late December 1944, von Rundstedt launched a counterattack which developed into the Battle of the Bulge. The use of the fuzes entered a new field, that of artillery fire against ground forces. The results of this usage were devastating to German troops and put fear into their hearts. No longer were their foxholes havens against shrapnel burst for with the use of the "funny fuze," as it was termed by General Patton, the shrapnel bursts occurred before the projectiles hit the earth, showering areas with high-velocity fragments.
The proximity fuze was one of the major contributions of American scientists, engineers, and manufacturers to the winning of the war. Security prevented them from receiving the plaudits they so well deserved but they had full payment in the knowledge of their own great contributions. General Benjamin Lear, USA, described it as "the most important new development in the ammunition field since the introduction of high-explosive projectiles." General George Patton, USA, likewise paid tribute to its developers, stating, "I think when all armies get this shell we will have to devise some new method of warfare." Patton's prophecy might well have come true except that within the year, this great electronic achievement of combined United States science, industry, and naval endeavor was dimmed by the development of greater and more damaging concentrated explosive power than the world had ever experienced. Even this development necessitated the continued use of the proximity fuze in the control of its point of detonation.
1 Rowland and Boyd, "U.S. Navy Bureau of Ordnance in World War II," Washington, Government Printing Office, 1953, pp. 276-278.
2 Ibid., p. 278.
3 The author, then serving in the U.S.S. Cleveland, was an eye witness to these firings.
4 Rowland and Boyd, op. cit., p. 283.
6 Ibid., p. 286.
7 Ibid., p. 285.
8 Ibid., pp. 286-287.
9 Ibid., pp. 288-290.
TOC | Previous Section: Chapter XL | Next Section: Chapter XLII