Interest in radio guidance dates back to the turn of the century. Notable pioneering efforts took place at the Hammond radio research Laboratory, a privately organized research group. Its founder, John Hays Hammond, Jr., an inventor whose “ . . . development of radio remote control served as the basis for modern missile guidance systems,” also “ . . . developed tech- niques for preventing enemy jamming of remote control and invented a radio-controlled torpedo . . .” [75]. By 1914, he was actively exploring means to “ . . . greatly minimize the possibility of an enemy determining the wave lengths used in the control of the craft and thereupon interfering with the control thereof” [76]. In the radio guidance of remote vehicles, Hammond was following in the footsteps of Adm. Bradley A. Fiske and of Nikola Tesla [77, p. iii]. (Note: See [44, ch. XXIX] for more background on Hammond, Fiske, and Tesla.) The efforts against jamming were, initially,
pursued by Benjamin F. Miessner, Hammond’s sole coworker during 1912, who had invented a primitive form of SS signaling [77, p. 32] which was quite likely the earliest to be thus “ . . . transmitted in a peculiar way” [77, p. 65].
The Miessner-Hammond carrier broadening was incorporated into a mil- itary transmitter, which with its associated receiver (that additionally intro- duced amplitude-limiting action) was delivered to the U.S. Army in France just before World War I ended. There, Maj. Edwin H. Armstrong verified the Hammond system’s ability to communicate in the face of powerful enemy interference, a challenge officially recognized as “ . . . one of the most impor- tant matters connected with the war” [78, footnote 48].
From the First World War on into World War II, the furtherance of wide- band techniques continued at the Hammond Laboratory, with concentra- tion on frequency-wobbling methods to send secret signals which sounded like “ . . . some new kind of man-made static . . . “ [78, p. 1203]. The anti-jam- ming attribute of spectrum spreading became obvious as the frequency devi- ation of the wobbling increased so that its “ . . . wider swing reduced the amount of time that a given narrow-band disturbance could affect the inter- mediate-frequency circuit of the receiver . . . “ [78, p. 1202]. Contributions of this kind, originating in that era from the Hammond group (additionally to [66]), are documented in patents on TR and SR wobbling which were filed, respectively, by Emory L. Chaffee [79] in 1922 and Ellison S. Purington [39] in 1930.
The Chaffee patent claims that his invention, involving “rapid and erratic”
wobbling, is useful for “secret radio telephony” and for “ . . . telegraphic sig- nals or radio-dynamic control.” With respect to the Purington patent [39]
(which seems somehow to have been overlooked in the chronicles [78] and [80]), that SR invention for obtaining “secrecy in which a rapid variation rate is necessary . . . “ for the wobbling was a sequel to Hammond/Navy exper- iments of 1921—1922 which “ . . . established points of interest regarding information theory when the interference greatly exceeds the signal” [78, p.
1202]. Also, circa 1920, the Hammond company had contracts from the U.S.
Army to show that “noninterferable characteristics” could be secured for the radio control of aircraft [80, p. 1262].
During World War II, the NDRC entered the realm of guided missiles with a variety of projects [81] including the radio control in azimuth only (AZON) of conventionally dropped bombs (VB’s) which trailed flares for visibility, radar-controlled glide bombs (GB’s) such as the Pelican and the Bat, and the remotely controlled ROC VB-10 using a television link. Now documented mostly through oral history and innocuous circuit patents, one of several secure radio guidance efforts took place at Colonial radio, pre- decessor of the Sylvania division at Buffalo, NY. This project was under the direction of Madison Nicholson, with the help of Robert Carlson, Alden Packard, Maxwell Scott, and Ernest Burlingame. The secret communications system concept was stimulated, so Carlson thinks, by talks with Navy
people who wanted a system like the “Flash” system which the Germans used for U-boat transmissions. However, it wasn’t until the Army Air Force at Wright Field posed the following problem that the Colonial Radio effort began seriously.
The airfoil surfaces of the glide bombs were radio controlled by a mother plane some distance away, sometimes with television display (by RCA) relayed back to the plane so that closed-loop guidance could be per- formed. It was feared that soon the Germans would become adept at jam- ming the control. To solve this problem Colonial Radio developed a secure guidance system based on a pulsed waveform which hopped over two diverse frequency bands. This dual band operation led to the system’s nick- name, Janus, after the Roman god possessing two faces looking in oppo- site directions. Low duty cycle transmission was used, and although the radio link was designed to be covert, the system could withstand jamming in one of its two frequency bands of operation and still maintain command control.
The Colonial Radio design’s transmitter for the mother aircraft was des- ignated the AN/ARW-4, and the corresponding glide bomb receiver was the AN/CRW-8. Testing of the radio guidance system took place at Wright Field in 1943, under the direction of Lt. Leonhard Katz, Capts. Walter Brown and Theodore Manley, and Project Engineer Jack Bacon. The contract, includ- ing procurement of two transmitters and seven receivers, was completed by June 1944 [82].
ITT also participated in these World War II guidance programs, notably with a system called Rex [63]. One patent, evidently resulting from this work and filed in 1943 by Emile Labin and Donald Grieg [83], is interesting because it suggests CDMA operation in pulse code modulation (PCM) sys- tems by slight changes in the pulse repetition frequency. In addition, the patent notes the jammer’s inherent problem of trying to deliver its inter- ference to the victim receiver in synchronism with the transmitted pulse train. However, the notion of multiplicity factor or spectrum spreading is not mentioned.
A third guidance system for the control of VB’s and GB’s was proposed by the Hammond Laboratory. The Hammond system used a complicated modulation format which included a carrier wobbled over 20 kHz to pro- tect against tone interference, and FM control signals amplitude modulated onto this frequency-modulated carrier [63]. More notable in this history than the system itself is the fact that Ellison Purington in 1948 came close to describing a TH and FH carrier for a radio control system in a patent appli- cation [84] (see Figure 2.6). The actual details describe a TH-SS system with control signals coded into the transmission using frequency patterns.
Magnetic or optical recording “on a rotating member driven by a constant speed motor” was one suggestion for the storage of different time hopping patterns, while another possibility mentioned involves delay line generation of pulse train patterns. Control keys are hidden in the way that the patterns
Figure 2.6. Purington’s time-frequency chart definitely suggests a hybrid TH and FH system. However, the illustrated transmitter uses the assignment of TH patterns to fre- quency tracks as a method for signal encoding. (Redrawn from [84].)
are mapped onto different frequencies to create “radiations . . . randomly distributed in time and in frequency.”
Other salient patents, based on World War II AJ and command/control efforts, include those of Hoeppner [85] and Krause and Cleeton [86].
In mid-1941 an application for the FH patent [87], [232] was filed by Hedy K. Markey (see Figure 2.7) and George Antheil. Neither inventor was an engineer, conversant with the prior art, e.g., the broad FH method [88]
invented a dozen years earlier. Being at that time a recent ex-spouse of Hollywood scriptwriter Gene Markey, Hedy Markey had been baptized Hedwig Eva Maria Kiesler. Growing up in Austria, this only child of a promi- nent Vienna banker had shown, at age 16, a flair for innovation by letting herself be filmed in total nudity while starring in the Czech-produced clas- sic,Ecstasy(the fifth of her many motion pictures [89]). Several years later she was one of the small minority among non-Jewish Austrians who saw great danger to the world in Germany’s early-1938 Anschlussof her home- land.That year, permanently leaving her country and her munitions-magnate husband, Friedrich A. “Fritz” Mandl, as washouts to Hitler, the actress came to the United States on a seven-year contract from Metro-Goldwyn-Mayer.
There, she legalized her stage-renaming (by Louis B. Mayer) to Hedy Lamarr. The now-escaped wife brought with her memories of company films,
Figure 2.7. Hedy Lamarr, inventress of the first frequency-hopping spread-spectrum technique explicitly conceived for anti-jamming communications. (Photo courtesy of Kenneth Galente, The Silver Screen, New York.)
which she had witnessed, of difficulties Mandl and his factory managers were encountering in getting their “aimlessly” unguided torpedoes to hit evasive targets.
Once settled in southern California but still greatly concerned by the war then impending for the United States, Lamarr sought out the versatile and volatile symphony composer Antheil [90, ch. 32]. Quickly stimulating a new application of his creative talents, she led him to their joint conception of a radio-control scheme in which the transmitted carrier frequency would jump about via a prearranged, randomized, and nonrepeating FH code. A torpedo carrying a properly synchronized receiver could thereby be secretly guided from its launch site all the way to its target. Hedy Lamarr and George Antheil thought such a stealthy “dirigible craft” capability, for missiles as well as torpedoes, would soon be needed by Germany’s opponents.
Drawing large diagrams while stretched out on Lamarr’s carpeted floor, she and Antheil concentrated on them for weeks until they arrived at a secure and feasible FH-SS concept. The system design took special advan- tage of the composer’s know-how, in their plan to synchronize the radio transmission and reception frequencies by means of twin, identically crypto- code slotted, paper music rolls like those used in player piano, audio- frequency (!) mechanisms (see Figure 2.8). Indeed, Antheil had already achieved such synchronization precisely in his multi-player-piano opus of the 1920s,Ballet Mécanique[90, p. 185]. Their invention disclosure points out that an FH repertoire of eighty-eight radio frequencies could readily be accom- modated.
The Lamarr-Antheil invention promised to be “sturdy and foolproof,” and well within the manufacturing capabilities of the 1940s, and its FH secrecy features were enhanced by the inventors’ advocacy of short-pulse trans- mission to provide low detectability. But what seems, for that day, to be most
Figure 2.8. Redrawn from the Markey-Antheil patent [87]. Upper figure shows mid- course corrections to a torpedo course, made by FH-SR-SS communication from an obseving aircraft. A “piano-roll” recording of the frequency hopping sequence is illus- trated in the lower drawing.
perceptive in the initial installment [91] of the invention disclosure is pre- sented quite boldly:
“. . . it is veritably impossible for an enemy vessel to ‘jam’ or in any way inter- fere with the radio-direction of such a previously synchronized torpedo because, simply, no ship may have enough sending stations aboard or nearby to ‘jam’
every air-wavelength possible or to otherwise succeed except by barest accident to deflect the course of the oncoming radio controlled torpedo—unless, of course, it happened to have the exact synchronization pattern between sender- ship and torpedo.
(Minor, mostly typographical improvements have been made here within this quote while dropping its originally all-capitals lettering; in the patent itself [87], “block control” is said rather than “jam.”)
Lamarr next brought her and Antheil’s secret system concept to the attention of the then newly government-established National Inventors Council, which soon (quoting from [92]) “ . . . classed Miss Lamarr’s inven- tion as in the ‘red hot’ category. The only inkling of what it might be was the announcement that it was related to remote control of apparatus employed in warfare.” That is how it was guardedly publicized by the U.S. Department of Commerce after being scrutinized by Charles F. Kettering, the noted General Motors inventor who was also a pioneer (with Elmer A. Sperry) in remotely piloted vehicles.
Despite this first reaction of enthusiasm mixed with caution, the Lamarr (Markey)-Antheil patent appears to have been routinely issued and pub- lished, curiously without imposition of a Secrecy Order. It may be that such potential restraint from the U.S. Patent Office was precluded by the fact that Lamarr’s continuing (until 1953) Austrian citizenship rendered her an
“enemy alien” during most of World War II. Although this personal cir- cumstance is indeed reflected in the patent case file [93], it seems to have been a mere technicality, which did not impair her screen-actress career or her image to the American public.
At one of the many war-bond rallies through which she expressed her loy- alty, Hedy Lamarr told a crowd of 10,000 in Elizabeth, NJ, that “. . . she knew what Nazism would mean to this country because she knew what it did to her native country, Austria. ‘I’m giving all I can because I have found a home here and want to keep it’ ” [94]. She had certainly tried to contribute to the war effort, too, by her inventiveness.
Lamarr and Antheil seem, however, to have been more than a score of years ahead of their time, considering that FH-SS evidently was not used operationally against intentional jamming until the 1963 exercise, by the U.S.
Navy, of the Sylvania BLADES system. It appears that no coded-paper-hole implementation ever resulted from their FH invention, and that in the decades since the issuance of its patent, whatever scant notice it has received has been confined to the popular press [95].
As far as technology is concerned, all of the above communication sys- tems share a common propensity for the use of electromechanical devices,
especially where signal storage and synchronization are required. Undoubt- edly in the 1940s the barriers to be overcome in the development of SS com- munications were as much technological as they were conceptual. The emergence of missile guidance as a potential weapon delivery technique requiring light-weight, rugged construction, did much to drive communica- tion technology toward all-electronic and eventually all-solid state systems.
Furthermore, the use of guided weapons placed communication jamming and AJ in a more serious light [52]:
Radio jamming, in World War II generally did not require, and did not receive, much attention. Everyone was far more concerned [for intelligence analysis]
with listening in. However, when . . . inhuman radio-guided missiles put in their terrifying appearance, the electromagnetic frequencies employed by the new military engines became suddenly too dangerous to neglect.