U.S. ARMY RADAR EQUIPMENT
Early Research and Development - 1918 - 1937
by H. M. DAVIS,
national defense of the United states within the meaning of the
Espionage Act, 50 17. S. C. , 31 and 32. as amended.
The transmission or the revelation of its contents
in any manner to an unauthorized person is prohibited by law.
Copy No. 27of35copies made
xiv plus 69pages and
Historical Section Field office
Special Activities Branch
Office Service Division
Office of the Chief Signal officer
Army Service Forces
THERMAL DETECTORS AND FISCAL OBSTACLES
Fort Monmouth, home of the Signal Corps Laboratories, is located only a few miles from the northern New Jersey coastline which reaches its extremity in Sandy Hook, at the entrance to New York Bay. On the Hook itself is the military reservation of Fort Hancock, part of the New York Harbor Defense, and on the adjoining mainland are various lighthouses and Coast Guard lifesaving stations. From these vantage points may be seen the continuous movement of sea-going craft, from fishing vessels to passenger superliners, in and out of the port of New York. Thus a ready-made outdoor laboratory was available for testing detection equipment against surface vessels which, for early experimental purposes, were more convenient targets than aircraft. The work of the Signal Corps Laboratories eventually was to be conducted along a twenty-mile segment of the Atlantic coastline from the beach resort of Belmar to the Coast Artillery battery parapets of Sandy Hook.
During the fiscal year 1933, a field testing base, was established at Battery Halleck, and inactive harbor defense battery near the point of Sandy Hook. About 30 feet above sea level, this site had a clear sweep of the transatlantic approaches through lower New York Bay. It was used for both thermal and radio position finding. Other detectors were set up at the Coast Guard Station at the beach resort of Sea Bright. Another base was established at Navesink Lighthouse, Highlands, N. J., on the mainland close to the sand-bar approach to Sandy Hook.1 Eventually a restricted area on Sandy Hook was to be for a considerable time the principal assembly and test zone for the first standardized Signal Corps radar equipment.
For the most part, these experimental installations were originally set up by direct agreement with the local authorities. In the case of Navesink Lighthouse, a formal request went from the Signal Corps Laboratories through the War and Commerce Departments for permission to install a searchlight on the grounds. 2
The Commerce Department granted the request on behalf of the Lighthouse
Service with the proviso that "in connection with the mobile searchlight
it is considered that since the same will be shown from the vicinity of
the light a Notice to Mariners should be issued in connection with its
use." 3 Accordingly,
just prior to the actual tests, a formal Notice to Mariners was sent out
by the office of Superintendent of Lighthouses, 3rd District Station Island,
N. Y,, reading as follows;
New Jersey - A searchlight will be used for experimental purposes at Navesink Lighthouse intermittently between 9 P.M. and 12 P.M. for several nights during the period between July 30 and August 9th, 1935. The searchlight will be used principally over an area extending some four miles southeastward from Scotland Lightship.
The notice bore the legend, "Please Post Conspicuously."' Apparently it served to crystallize local gossip, for shortly after it was made public, the Long Branch Record, the newspaper nearest the scene, carried an article under the headline;
RAY WHICH DETECTS SHIPS OFF SHORE TO HE TESTED SECRETLY AT HIGHLANDS.The story said that "plans of the army to conduct a series of tests were revealed in a bulletin of the Bureau of Lighthouses containing instructions to mariners." 4 The item was picked up by correspondents for larger newspapers, among them The New York Times, whose headline read;
MYSTERY RAY SEES 'ENEMY' AT 50 MILES.This and other dispatches were actually speculative in content. It was noted that Coast Artillery troops had arrived with
:searchlight, that visitors and reporters were stopped on the road leading to Navesink Lighthouse, and that Colonel Blair of the laboratories would not comment on the purpose of the activity. 5 The text of these dispatches contained no specific military information and consisted largely of guesses based for the most part on the already discarded method of reflected infra-red rays. But these articles, and the comments on them in other publications, did attract public attention to a secret project, and it is possible that they served to stimulate interest on the part of other powers. The only available evidence to that effect is a letter
- 26 -
MAP OF REGION USED BY SIGNAL CORPS LABORATORIES
The proximity of Fort Monmouth to the New York Harbor entrance provided
a ready-made outdoor laboratory for tracking surface vessels. Many famous
transatlantic liners served unwittingly as experimental targets of early
addressed to the Signal Corps Laboratories on the letterhead of
"Okura & Company, 30 Church Street, New York, main office Tokyo, Japan," reading as follows:
We are very much interested in the "Mystery Ray" device described on page 29 of the October 1935 issue of "Popular Science Monthly" which we understand you have developed. We shall, therefore, appreciate it very much if you will kindly send us at your earliest convenience any further information regarding the "Mystery Ray" that you can. 6
The Signal Corps reply, signed by Lt. Col (now Major General) Roger B. Colton, was: "I regret to inform you that no information of the kind requested by you can be furnished."
The "further information" which was withheld at the time from Okura & Company in particular, and from the public in general, is as follows. During the two years preceding the Navesink Lighthouse tests of August 1935, considerable progress was made in the "one-way" method of heat detection. The difficulty with background temperature, such as the heat radiated from clouds, which had been a serious obstacle to the work of the Frankford Arsenal, was partly overcome by the use of a compensated thermopile. The compensation consisted in using, not one set of thermocouple junctions, but two sets of them side by side, so connected that voltages generated by heat falling on both sets would be in opposition and thus give a zero indication. If, however, the image of a heat-radiating target fell on only one of the two sets, there would be an indication. Two such compensated thermopiles were delivered in March 1934, from the Eppley Laboratory, Inc., of Newport, R. I.
To obviate another source of error, due to local air currents which would heat or cool the thermopile by convection, the Signal Corps Laboratories experimented with windows designed to transmit only distant radiation. Windows of glass, quartz, mica and other transparent materials were tested and commerical sources of these materials were canvassed.
In April 1934, an Eppley compensated thermopile in a 60-inch parabolic metal reflector was setup in a seacoast searchlight mounting at Battery Halleck, Fort Hancock, overlooking the commercial channel to New York. During the ensuing months tugs, freighters, tankers and small passenger boats were picked up and followed to distances of 5,000 yards in drizzling rain, 10,000 yards in fair
weather. Two big liners - the German Bremen and the British Olympic - were tracked on the outbound ocean course to the horizon 20,000 yards away. 7 At dusk on 26 September 1934, the Mauretania was tracked long after she had disappeared into the haze to a distance of 23,000 yards.
In November 1934, the laboratories obtained two 1934-model 60-inch Army searchlights. One of them was modified into a thermolocator by removing its arc-light mechanism and replacing it with a thermopile unit thus converting a transmitter of light into a receiver of heat. In order to amplify the feeble electric current generated in the thermopile, a mechanical switch was installed, operated by a cam on a motor, which opened and closed the circuit 90 times per second. A four-stage amplifier was peaked also at 90 cycles per second. A portable searchlight was used to check on the accuracy of night pick-ups. 'this was the outfit installed at Navesink Lighthouse in the summer of 1935 which drew the attention and inaccurate speculation of the press. Although at that time "radio-optical" rays were already being used for detection (Below, Chapter V) the particular "mystery ray" used in 1935 at Navesink Lighthouse was not a ray at all; it was simply a detector receiving the heat radiation given out continuously and involuntarily by all types of ships.
With this equipment large tankers and freighters were easily picked up leaving. or entering Ambrose Channel, 13,000 yards away. On 22 June 1935 the 79,000-ton Normandie (now the U.S.S. Lafayette) was tracked on a clear afternoon to a distance of 30,000 yards, when it was lost due to interference from closer vessels. On the night of June 24 the 30,000-ton Statendam was also tracked to 30,000 yards. The following afternoon the 45,000-ton Aquitania was tracked with the thermolocator to 18,000 yards, although a rapidly changing fog had by that time reduced optical visibility to 8,000 yards. 8
The early phases of the above mentioned work were conducted with such a high degree of secrecy, and apparently with such a lack of coordination by the higher echelons of the War Department, that two branches of the Army for a time conducted development of the same type of device without being aware of the duplication. The other branch involved was the Corps of Engineers, which was responsible for development and procurement of searchlights.
1935-MODEL SOUND LOCATOR
Development of heat or radio detection equipment was made urgent by the breakdown of sound location at maneuvers of Army antiaircraft and Air Corps units in 1933 and 1936. This photograph shows a sound locator used at First Army Maneuvers, Pine Camp, New York, in August 1935.
Signal Corps Photo 103030
The theoretical objections to sound locators, which were discussed in Chapter I, were confirmed during joint antiaircraft Air Corps exercises held at Fort Knox, Kentucky, in May 1933. As a result of criticism of the searchlight-control system, the Chief of Engineers proposed that a competent commercial concern be engaged to develop a suitable means of detecting the approach of airplanes by means of the hot gases emitted from the aircraft engine. The proposal was approved by The Adjutant General, and in December 1933, the Corps of Engineers entered a contract with the General Electric Company at a cost of $100,000 for development of a heat detector. 9
It apparently was not understood at the time by either the War Department or the Corps of Engineers that a similar project was already under way in the Signal Corps Laboratories, and the Signal Corps did not know of the work by the Corps of Engineers.10
The duplication of effort was disclosed in June 1934, as a result of a letter to the War Department from the Commanding General, Hawaiian Department, recommending that an investigation be made of the use of ultra-violet rays to detect the approach of enemy transports. Reference of this letter to the Signal Corps elicited the comment that surface craft already were being detected by radiant heat. The Chief of Coast Artillery, on behalf of the using arm, thereupon called the Chief Signal Officer's attention to the similarity between the Signal Corps and Engineer projects and urged that steps be taken "to insure that there will be no interference, duplication, or division of responsibility in carrying out this development." 11
In reply, the Chief Signal Officer, Major General Irving J. Carr, cited the history of the Signal Corps project since 1930 and recommended that the Engineer contract with General Electric be turned over to the Signal Corps in accordance with Army Regulations 105-5, which made the Signal Corps responsible for development of "electrical apparatus associated with direction finding for determining the location of... aircraft and ... all the electrical apparatus associated with range finding."12
fr Chief of Coast Artillery to CSigO, file OCCA 413.684/AF, Subj: "Development
of Heat Detection Device," S.C. reference file OCSigO, 311.6(6-4-34). This letter, and twenty-six indorsements which it accumulated during nearly two years, documents most of the history of the jurisdictional issue until final assignment of the entire project to the Signal Corps. In the balance of this chapter it will
be referred to by the subject title only. Office of the Chief of Engineers purchase order yo. 4673, ref. V 978-eng-556, 11 December 1933.
The Chief of Engineers, Major General E. M. Markham, by indorsement to the same letter, voiced objection to relinquishing the General Electric contract. Recalling that the original development of listening apparatus for locating airplanes was carried on by the Corps of Engineers during the first World War, although later transferred to the ordnance Department as a fire control item, and pointing out that the development and procurement of searchlights was still an Engineer responsibility. General Markham wrote:
The maneuvers at Fort Knox in the summer of 1933 demonstrated an almost complete breakdown in the location of airplanes by sound due to effective means of silencing the approaching planes. It was evident to all observers that some other means of locating airplanes had to be developed at once. The allocation of this problem to the Corps of Engineers by the War Department seemed logical as the searchlight, its controls, and its detection equipment all form one mechanical unit and must be carefully coordinated if the best results are to be obtained.Thereupon the Chief Signal Officer withdrew the original request to take over the Engineer contract and recommended that the Signal Corps be relieved entirely of the project of detecting aircraft by heat radiation, "and that this project be assigned permanently to the Chief of Engineers."
The higher authorities of the War Department, however, were not prepared to take such a step. Instead, the project was temporarily divided between the two branches along functional lines. The Chief Signal officer was to be responsible for detection of marine craft, both by subaqueous sound ranging and invisible heat radiation, and the Chief of Engineers was made responsible for detection of aircraft. Reports of progress after a year's development by the two services were to be compared; after which a decision would be made by the Secretary of War as to the final responsibility.13
The work of the Signal Corps Laboratories on heat detectors during the time this correspondence was going on has been discussed in Section C. above. Early in 1936 the heat detector which had been used at Navesink was transported to the headquarters of
- 30 -
HEAT DETECTOR FOR POINTING SEARCHLIGHT
This photograph shows the ultimate combination of the Corps of Engineers and Signal Corps heat detectors, as used in conjunction with radio detection in 1937. Thermopiles and control equipment designed by the Signal Corps Laboratories were mounted in a mechanical structure previously built by the General Electric Company on an Engineer Contract. As operated in 1937, the heat detector received directional data from the radio equipment (part of one antenna may be seen at right) and in turn controlled the pointing of a searchlight.
SCL Annual Report FY 1937, fig. 3
Signal Corps Radar - Chapter IV
the Coast Artillery Board at Fort Monroe, Virginia, for a secret comparative test with the heat detector built by General Electric for the Corps of Engineers. The Signal Corps was represented by Lt. Col (now Major General) Roger B. Colton, Dr. S. H. Anderson and Dr. (now Major) H. A. Zahl. The Signal Corps detector, which was designed for use only against marine targets, picked up the Mine Planter Schofield through a smoke screen, showing an azimuth accuracy of 0.015 degree at 10,000 yards range. It also picked up and tracked a B-6 bomber. The Coast Artillery Board concluded:
Both the Signal Corps and Engineer detectors have sufficient reliability of performance for use under service conditions against marine targets. Both detectors have sufficient accuracy in direction. Range of either detector was in excess of the range of effective illumination by a searchlight, regardless of weather conditions, but short of the ranges theoretically possible based on considerations of height of site and curvature of the earth alone. The heat detector is an auxiliary of considerable potential value for seacoast defense.The Board held that either of the two models, which were essentially similar, could detect marine targets in darkness and serve to direct a searchlight. Neither, however, was considered adequate for detection of aircraft, and both were considered insufficiently developed for fire control purposes. The Board recommended that research and development of the heat detector be continued with high priority.14
Even before this recommendation was made, however, official interest underwent a shift to radio detection. This was occasioned partly by wider acquaintance with the Navy's concentration on that method. The Chief of Engineers, in submitting to the War Department the required report on heat detection progress on 20 November 1935 called attention to the Navy's development and pointed out certain "inherent limitations" in thermal detection, such as the false indications from clouds and the obscuring effect of atmospheric moisture. Again the Chief of Engineers sought authority to carry on the development, this time by the radio method. 15
The Chief Signal Officer - Major General J. B. Allison had succeeded to the post - was now provided with a new reason for seeking control of the development. "There is but a single medium,"
he pointed out, "for the transmission of radio. For this reason it is a cardinal principle that every endeavor must be made to centralize control of radio matters in a single agency wherever practicable. Such centralization is practicable in the army and the Signal Corps is therefore definitely and properly designated by the provisions of AR 105-5 as the agency in charge of radio development. The introduction of another agency could not fail to produce the utmost confusion and inefficiency in all uses of radio, whether these uses be concerned with general signal communications, aircraft navigation, or aircraft detection. The radio method now proposed by the Engineer Hoard is entirely familiar to the Signal Corps, it having first been examined into in 1931 ...." 16
At this point a third bidder appeared. The Ordnance Department, which had voluntarily relinquished the project to the Signal Corps in 1930, now argued (with some prophetic insight) that the data from a short-wave radio detector might eventually be applied directly to the gun director, eliminating the searchlight and replacing the sound locator. On this basis, it was recommended that "the Chief of Ordnance be now charged with responsibility for the development of short-wave radio locators for aircraft as improvements upon the sound locator, and that any available funds be transferred to the Chief of Ordnance to permit early prosecution of the work. l7
This proposal was ignored by the War Department. Instead, the Chief of Coast Artillery was directed to draw up military characteristics for devices for detecting marine surface targets and aircraft by means of either heat or radio. On 29 February 1936. these military characteristics were transmitted to the Chief Signal Officer by The Adjutant General with the directive:
"The Signal Corps is charged with the further development of each of these detectors ....It is desired that the development of these detectors be given the highest priority practicable, with particular emphasis on the development of the detector of aircraft.18
Here was the official go-ahead signal. The green light was on. But before there could be real full-speed-ahead, the engine needed fuel-in the form of substantial government funds. On
this score, difficulties remained. This was 1936. On 16 March 1935 Germany had reinstituted military conscription in defiance of the Treaty of Versailles. On 7 March 1936, the German Army reoccupied the Rhineland. Japan was consolidating her Manchurian springboard for attack on North China. Our ultimate enemies were preparing with all their resources for total war. But in fiscal year 1936, the entire expenditure of the U. S. War Department was only $382,588,002, and the funds available in the following year were slightly less.19
In 1936, the Chief Signal officer sought for research and development on the aircraft detection project, and failed to obtain, a sum of money less than the subsequent procurement cost of a single Radio Set SCR-268•
The Chief of Engineers had indicated, in connection with the question of jurisdiction, that $19,500 of funds appropriated for searchlights had been set aside for airplane detection development.20 But, although the project itself was transferred to the Signal Corps, the Chief of Finance ruled that the funds could not legally follow, on the ground that an appropriation for "Engineer Service, Army," could not properly be applied to a project now redefined as belonging to "Signal Service of the Army." 21
The chief signal officer now requested that the War Department make available $40,000 for the project for fiscal year 1936 and 1937, obtaining it, if necessary, by a special request to Congress.22 The reply, by order of the Secretary of War, was negative, at the same time re-emphasizing the importance of the project;
The funds setup for research and development of Signal Corps projects are considered sufficient in view of the many other pressing needs of the army. The development of an efficient means of detecting the approach of aircraft is considered of such vital importance to all branches of the Army that it is considered essential to place it in the highest. priority- It is therefore directed that the Chief Signal officer provide the additional funds required for the development of the detection of aircraft by a reduction in the amounts now setup in the fiscal years 1936, 1937 and 1938, for less urgent projects. 23
Treasury figures quoted in The world Almanac.
20 "Development of Heat Detection Device," 12th Ind., 20 November 1935•
21 Ibid., 22nd Ind., 30 March 1936.
22 Ibid., 25th Ind., 20 Aril 1936.
23 Ibid., 26th Ind., 1 May 1936.
Repeated further requests for additional funds were made by the Chief Signal officer and were strongly supported by the Chief of Coast Artillery. The urgency of .the detection development was re-emphasized by the lessons of joint Antiaircraft Air Corps Exercises held at Fort Belvoir, Va., in April and May 1936 with the sound locator still serving as the standard device for locating hostile planes. A Board of officers appointed by the Secretary of War reported that "detection and location of bombing planes of the Type B-10B ,(Martin Bomber) used in these tests at night by means of the present sound locator is impossible at altitudes greater than 15,000 feet; at 12,000 feet and less, these planes can be detected and illuminated only about one course out of three." Citing these observations, the Chief of Coast Artillery wrote:
I hold that the Army has before it today no more important development project than that of finding positive means for the detection of aircraft ...Any development of high priority requires funds for vigorous prosecution... It is recommended that the Chief Signal officer be provided at an early date with the funds necessary to enable him to proceed vigorously with this most important development work.The War Department agreed in reply to this that the development was indeed "of vital importance to all arms of the service" but reiterated its previous ruling by instructing the Chief Signal officer that "funds for the vigorous prosecution of this development must be provided by the curtailment of other less pressing developments. " 24
The other developments under way at that time in the Signal Corps Laboratories included fundamental research, service testing and improvement on many items which were to become important in the tactical signal communications of World War II - among them the first field artillery and infantry walkie-talkies, the vehicular radio sets SCR-193 and SCR-245, a shielding system for suppressing radio interference in tanks, the sound-powered telephone, the throat microphone, improved field telephones, field wire, assault wire and loading coils. Although physical facilities for this work had been greatly improved by the opening of the new Squier Laboratory building at Fort Monmouth, the personnel on 30 June 1936 still consisted of only eight officers, seventeen enlisted men and ninety-two civilians. The communications development work of the Signal Corps is to be chronicled in another historical study, but the projects are mentioned here
to illustrate the nature of the "other less pressing developments" from which funds and personnel had to be diverted into the high priority detection program.
Out of fiscal year 1937 funds, in compliance with the War Department directive, $75,741.74 was diverted to aircraft detection, as compared with a total of $133,748.54 expended in the same period (up to 1 May 1937) for the thirty-eight other development projects of the laboratories. 25
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