This is the continuation of a story begun on our August 2013 Home Page. To go to an archived version of that page, click here: August 2013 Home Page Archive. To return to this month's actual Home Page, click on the Signal Corps orange Home Page menu item in the upper left corner of this page.

continuing...

Foundationally, wire was ideal for supporting three modes of communication: telegraphy, telephony, and a new form of communication then coming along called teletyping. As most of our readers know, telegraphy involves sending messages in Morse code. The telephone on the other hand, as all know today but many did not back then, deals with carrying the human voice over wires, as a means of communication. Teletypewriters of the kind back in those early days transmitted messages by printing them out on either inked paper, or in the form of perforated symbols along a paper tape. This latter form of printed output held the added advantage of allowing the teletype operator to use the paper tape created for multiple transmissions, by inserting it into a paper tape reader which could then retransmit the message on to other stations.

What the Signal Corps saw back then was that each of these forms of wire based communication had advantages for use in the battlefield, advantages that needed to be preserved if communication was to evolve from being strictly wire based to also include radio based forms. And so the Signal Corps set out to assure that for each of these three methods of communication there was a radio equivalent under development.

As development efforts moved forward to find wireless equivalents of the trinity of telegraphy, telephony and teletype, it soon became obvious that several new variants showed promise. The first of these was obviously radiotelephony, as nothing seemed quite as reassuring to someone in combat receiving orders than hearing the other person’s voice on the handset. Because of this, radiotelephony received most of the research effort the Signal Corps expended in this area.

Yet while radiotelephony was the darling child of the group, radiotelegraphy was clearly the easiest to develop from a technological standpoint, and so while research in other areas continued the work done with radiotelegraphy moved along the farthest and fastest. In fact, so quick was the development process for radiotelegraphy that units able to be tested in the field were the first to appear, offering high speed code transmission long before voice telephony was ready for use.

Following shortly on the heels of both of these, radioteletype began to move forward, although by the late 1930s it was still considered too new a form of wireless communication to be taken into account as a possible future battlefield communication platform.

Instead, wire telegraphy was the dominant communication form for the battle field, with the six-pound manual telegraph set TG-5 being one of the most prolific items in use up through and well into World War II. Part of the reason for reliance on telegraphy versus telephony came from the fact that the voltage of telegraphs like the TG-5 could be increased in order to drive the signal out over a greater length of wire, or to compensate for poor wires that might suffer from high resistance points along the length of the circuit. This could not be done with telephony, which required a rather precise voltage level, thus making telephone units less reliable in field locations. Add to this the fact that interference had less of an effect on a telegraph signal than on voice communication, and the fact that while telegraphy required a trained operator the enemy at least needed one too, as well as one who spoke English and knew Morse code, and it was easy to see why most military commanders trusted their front line communication to telegraphy.

Further back in the rear however, as the late 30s gave way to the early 40s and the onset of WWII, wire teletype began to be replaced the wire telegraph. And not surprisingly, wherever radio telegraphy made its appearance it pushed out wire telegraphy for good. The reason was obvious, the battle space included many areas where wire simply could not be laid, whether because of the terrain or the enemy. Either way, sending a radiotelegraph signal up into the air and over the obstruction provided a no-brains solution to the problem. Notwithstanding all of this however, wire based telephony still held its own, and proved the dominant form of voice communication for the time. Thus as WWII got underway the U.S. military, and most of its Allies, found itself depending on wire telephony, wire teletype, and radio telegraphy for battlefield-to-rear echelon communications.

To keep all of this wire based communication equipment working, the Signal Corps settled on a standard “field wire” which it called the W-110. At the same time, it used a different form of wire for combat field conditions, calling it “assault wire” and giving it the model number W-130. Not surprisingly, “field wire” proved heavier and more durable than “assault wire.” Either way, both were relatively light in weight, and composed of twisted pairs. However, the desire to keep the weight of the wire as low as possible caused both to exhibit limited capacity as well as range. On the other hand, because of their low weight they could easily be laid from reels carried by trucks, jeeps, or even horses and donkeys. As an example, a mile of twisted-pair “field wire” weighed 130 pounds, with the same amount of “assault wire” coming in at only 30 pounds.[1]

Not surprisingly, the reels the wire was wound on came in different sizes. On the smaller side, a two man crew could easily carry one with an axle through it, spinning it as they walked in order to lay out the wire. Once such axle, the RL-27A, weighed only 5 pounds. The RL-31 on the other hand, an A-frame like platform with a hand crank, cross braces and a brake, weighed 30 pounds. Even larger, the gasoline-powered RL-26 weighed in at around 600 pounds when loaded with two miles of W-110, and accordingly needed to be vehicle mounted for use.

     Wire & Wireless Research & Development

As to the devices connected to field laid wire, on the telephony side most were battery-powered and operated just like commercial ones of the time. The most common of these was the EE-8, EE-8-A, and later the EE-8-B, each a sound-powered telephone that worked based on the very first principles Alexander Graham Bell depended on when he invented the telephone. The first version of these had a bell, which obviously worked only to give away one’s position to the enemy… so later versions replaced the bell with a small light to signal an incoming call. Similarly, the early versions that came to the field sported well made, strong and rather handsome leather cases… these soon fell by the wayside in favor or corded fabric cases, as rationing took hold during WWII.

Most of these phones were connected to field switchboards, and while improvements were made in everything from the wire itself through to reels and the telephone instruments, little change occurred with regard to the switchboards used. From the Signal Corps’ standpoint, while some improvements could surely have been made, there were much more important areas where technological improvements needed to be addressed, and so battlefield switchboards were simply set aside as a priority. After all, they worked, and everyone knew how to use them.

Operationally, between the wars and on into WWII, three primary types of switchboards were used, all spin-offs of the French models that were prevalent during World War I. Classified in terms of the number of lines each could handle, they broke down into a 6 “drop” unit, a 12 drop unit, and a 40 drop unit.

The BD-71 (“BD” standing for board) had 6 drops. Its larger cousin, the BD-72, had 12 drops. Both found use as regimental boards, with the smaller being used at Company and Battalion levels too. Division level communication generally fell to the task of a 40-line unit called the BD-14. From a size perspective, all of these were small in stature. From a weight standpoint however, all of them were heavy, as they depended on dry cell storage batteries to operate; dry cell storage batteries being a necessary element of the operational aspect of the common battery system that Bell invented.

Thus, the system worked by powering itself off of both the local dry cell battery associated with the telephone instrument at the end of the wire, as well as the battery associated with the switchboard itself. In fact, that’s where the term “local battery” came from. If you did not have a functioning battery on your local instrument… be it the EE-8 telephone or the BD-71 switchboard… you were not going to communicate with the person at the other end of the line.

As most readers know, to make a call the originator cranked a handle that “rang up” the switchboard operator. Similarly, once it was determined by the switchboard operator who the caller wanted to be connected to, he or she would crank up enough energy on the switchboard to ring the telephone of the person being called.

As to the term “drop,” it comes from the device that notified the switchboard operator that there was an incoming call. Located in a small shutter above the jack opening that the switchboard operator plugged into to answer or initiate a call was an electromagnet (a.k.a. solenoid) that, when energized, dropped the shutter as a signal to the operator that there was a call. The hand cranking of the telephone on the other end of the line provided the voltage needed to energize the electromagnet and release the shutter.

Recognizing that on the upper end, the 40 line capability of the BD-14 would not be enough to take care of Corps or Army sized units, the Signal Corps developed larger switchboards to serve these needs. One of the switchboards the Signal Corps developed became known as the BD-89, and fit the niche size of commands that had outgrown traditional Division sized structure, but were not yet up to the full complement of a Corps. This unit provided a 60-line capability, yet was still compact enough to avoid making it necessary to augment the staff required to operate it.

Built in a modular fashion, the BD-89 was just one of many examples of how the Signal Corps brought modern manufacturing to the military between the wars. By making the unit modular it could be set up in a small configuration and added onto as the HQ unit grew. While today this may seem like common sense, back between WWI and WWII introducing newer forms of thinking to the art of product development was unheard of, especially in the military. Not so for the Signal Corps, as we said in the first part of this article last month, the Signal Corps was so advanced back then that it may have singlehandedly changed the outcome of WWII and made America the Superpower it is today.

To make assembly of a field switchboard easier, the Signal Corps grouped equipment into sets. Thus for a field army a set of equipment known as the TC-1 came into being. It consisted of a switchboard, the BD-80, a BE-70-F test cabinet, BD-90 power panel, BE-75 AC power distribution cabinet, BE-72 DC power and test cabinet, RA-36 rectifier, FM-19 protection panel, and a set of ME-4 maintenance equipment. Like other modular units the Signal Corps developed, the TC-1 could be installed in six sections, side by side until its maximum capacity of 100 lines was attained. While designed for field combat use, when installed the unit looked no different than any of the central office switchboards that could then be seen in any of the cities the Bell System was serving across America.[2]

Similarly, the equipment that found use in the wire telegraph and teletypewriter hubs in the military looked for all practical purposes just like that seen in the offices of Western Union, the great 1851 company that set out to and successfully wired America for telegraphy.

- - - - -

Back in the early 1930s, as the Signal Corps began looking seriously at how teletypes could be improved for use in combat, experimentation took place with systems that were called “telegraph printers” and which printed the message on paper tape. Later, as page teletypes replaced tape in the commercial world, the Signal Corps followed along and began to experiment in this area too. Around about then the term telegraph printer fell by the wayside, in favor of the more simple term teletype. To speed its development efforts the Signal Corps struck research agreements with the Teletype Corporation, a subsidiary of the American Telephone and Telegraph Company's Western Electric manufacturing arm. This company was selected because of several factors, not the least of which was that it had some of the best equipment then available, had the backing of the enormous AT&T and Western Electric companies and their laboratories, and was closely allied with some of the more powerful industrialists of the time. After all, a little power politics never hurt anyone, including the Signal Corps.

In short order what the Signal Corps decided to do was simply to alter, albeit only slightly, the Model 15–KSR built by The Teletype Corporation for commercial use and sale. This new system then became known as the TG-7, and became a standard for the U.S. military [see picture below].

Having everything needed from a power supply to spare parts, the TG-7 became the standard element for both the mobile field teletypewriter, known as the EE-97, and the fixed equipment teletypewriter, the EE-98. One of the changes that the Signal Corps required to be made by The Teletype Corporation to its original 15-KSR design however was to move to a layout that used what was known as a “neutral system.”

The neutral system, as opposed to the "polarential system" used in the 15-KSR, used fewer parts, thus reducing both wear and tear and the number of breakdowns. Just as importantly, the changes the Signal Corps requested added to the speed and accuracy with which the system transmitted messages. In the case of the TG-7 the neutral system’s operation alternated pulses of current with breaks when no current flowed. This caused each letter the transmitting operator struck on his keyboard to be translated, according to a five-unit code, into a combination of current flow (mark) and current break (space). On the other end of the line, at the receiving teletypewriter, this combination of codes actuated the same exact corresponding combination of key strikes, causing a near instantaneous printing of each character. When set side by side, one could see the nearly instantaneous reproduction of the message on the receiving unit, in synchronization with the transmitting teletypewriter’s keys being struck. Overall, the speed and accuracy of the system's operation was impressive.[3]

And so the Signal Corps improved on the technology of the day—sometimes in small ways, sometimes in big ways, but always an improvement­—improvements born out of the unique strategic alliances the Signal Corps struck between the wars with American industry, the country’s university research facilities, and within the Signal Corps' own 17 laboratories.

One example of how the Signal Corps turned these alliances to its advantage can be seen in how it went about fixing one of the biggest problems it faced in the early development of military field teletypewriters. That problem was the availability of reliable power, of a type that provided the stable flow of current needed to assure the integrity of the “mark-and-space” operation.

Research showed that the AC cycle rate required for stable operation of a teletypewriter could be anything between twenty-five Hz and sixty Hz, just as long as the rate was unvarying. So sensitive was the system’s operation that a shift of as little as 3% in the frequency would affect the accuracy of the output being printed. The reason for this was that the electrical impulses needed to keep both the sending and receiving printers in perfect synchronization had to be in synch themselves.

The Signal Corps tried many of the products of the time, looking for power units that would meet the close tolerance requirements, but none met the challenge. After testing six of the more well designed commercial units available, the Signal Corps set out to design its own. The result was a field generator that became known as the PE-77, a 70-pound DC generator that proved extremely reliable. To supplement this DC version the PE-75 was also introduced. It weighed in at 300 pounds, and provided commercial grade AC able to power the EE-97 mobile teletypewriter set.[4]

     Conclusion

One can see from all of this how determined the Signal Corps between the wars was on improving the equipment that would be available when the next world war rolled around. Since wire was the primary means of communication used to hold a battlefield together at that time, and because so much of the activity that surrounded field combat took place in rear-area administrative regions, it was only natural that the Signal Corps gave wire based forms of communication as much attention as it did. But it did not end there.

As the Signal Corps learned in WWI, the reliance on well protected rear-areas through which it could safely string its wire and keep it intact was quickly becoming a thing of the past. Better artillery, aircraft bombing runs even of the limited type seen in WWI, and other forms of advanced combat all combined to cause the Signal Corps to see the writing on the wall.

To prepare for the next big war, the Signal Corps not only focused on improving its wireline forms of communication, but embarked on a whole new program to supplant wire with wireless. In particular, in that no-man’s land of communication traffic that fell between Company, Battalion, Brigade, Division and Corps level combat operations the Signal Corps found much room for improvement in getting the message through. To solve the problems it saw, it set about researching, developing, building and bringing to the field some of the best radio telephony systems ever introduced. Next month we will continue this article by looking at the radio equipment that the Signal Corps brought to combat just in time for WWII. 

 

             

Footnotes

[1] For specifications on the types of wire used by the Signal Corps during WWII, visit this link: Standard Assault Wire. - To return to your place in the text click here:

[2] For a list of the various types of Army telephones, switchboards, and central office sets visit this link: Army Telephone & Switchboards. - To return to your place in the text click here:

[3] The “neutral system” lacks a relay block, polar-neutral key, motor control relay, and a terminal block, all of which are included in the commercial version. The military version also comes packed in two chests. One chest serves as an operation table for the printer, and the other as a seat. - To return to your place in the text click here:

[4] The EE-98 was identical to the EE-97 except that it lacked its own power unit (i.e. the PE-75). Being intended for fixed use, it was simply plugged into whatever commercial power was available. - To return to your place in the text click here:

Additional Sources

General information gathered from the following Signal Corps Information Letters: No. 1 (April, 1934), pp. 7 ff., No. 10 (July, 1936), pp. 13-17, No. 13 (April, 1937), pp. 8-9, No. 15 (October, 1937), p. 7, No. 18 (July, 1938), p. 12, No. 22 (July, 1939), p. 12, No. 24 (January, 1940), p. 9.

Additional general information gathered from Signal Corps Technical Letters: No. 38 (January, 1945), p. 24.

Data on the structure of the SCL network gathered from the SCL, Annual Report, 1936, pp. 21-22, 1937, p. 31, 1938, pp. 33 ff., 1939, pp. 42 ff., 1941, pp. 30-31.

Operational information about the Signal Corps Laboratories gathered from the Historical Report of the Signal Corps Engineering Laboratories, pp. 149-56, 161-62

Information on the differences in various types of Signal Corps field wire gathered from a report entitled "Rpt, C&E Coordination Bd OCSigO to Chief Com Coordination Br, 26 May 42, sub: Case 17 types of W-110 concentric vs. parallel lay” wire tests.

Additional general background information taken from the report by Major General Roger B. Colton, entitled Army Ground Communication Equipment, Electrical Engineering, LXIV, No. 5 (May, 1945), pages 173-74.

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