|IBM Radiotype at US Army Signal Corps Communications
in the Pentagon, 1944.
Photos in this section: IBM.
|IBM Radiotype - another view
|Radiotype Army demo 1942
|Pentagon comms center 1944
|Radiotype transmitting typewriter
Developed in 1931 by Columbia-educated Walter S. Lemmon, president of Radio
Industries Corporation in New York City, the Radiotype transmits text
messages from one electric typewriter to another via shortwave radio or
wire, and was widely used by the US Army Signal Corps during World War II.
The large photo shows the component parts. Top: Copy holder, transmitting
typewriter, paper-tape punch, control panel, receiving typewriter, clock
counter. Bottom: Automatic tape reader, tape winder, Morse code keys. WAR
(under the Control Panel label) was the call sign of the central Signal
Corps radio station.
shots from the Hollywood movie Air Force
Howard Hawks, 1943 (the full 2-hour film online for as long as the link
lasts). It features not only the IBM Radiotype and other IBM equipment but
also early-model B17s (and false propaganda involving Japanese-American
fifth-columnists in Hawaii). As the film opens (at 1 minute and 40 seconds)
in the "Base Signal Office" some clacking is heard and the sergeant goes
over to the Radiotype machine that is receiving a message. We see the
machine typing the message using a typewriter-like mechanism. He carries it
into the Base Intelligence Office and hands it to the captain, who hands it
to a codebreaker, who sits down at an IBM 032
, transcribes the message, and we see two punched cards come
out. The captain takes the cards and sticks them into the hopper of what
seems to be an ordinary IBM 405
, and we see the
clear-text message being printed by the 405's type bars, and this message is
what sets the plot in motion.
|1. Incoming message on Radiotype
|2. Closeup of message
|3. Transcribing onto cards
|4. Closeup of IBM 032 card punch
|5. IBM 405 type bars
|6. Message coming out of 405
Thanks to Henry "Strontium Black Cat" for most of these screen shots.
Military Messaging in World War II
Throughout World War II US, British, German, Japanese, and other armed
forces kept their widely scattered units and command chains in touch by
various means including short-wave radio. For the USA, the IBM Radiotype
was an important means of short-wave communication as it allowed messages to
be sent and received in real time as text, rather than (say) morse Code,
thus eliminating the need for specially trained human telegraphers at both
ends of a connection (such as
, who were both Navy radiomen during the war). But since enemy
forces could tune in to the US frequencies (or tap US wires), all messages
had to be encrypted. Therefore, great efforts were expended on all sides to
create unbreakable ciphers and develop methods of breaking intercepted
enemy ciphertext. Incidentally, there was no encryption equipment at the point
of origin; Signal Corps operators used closely guarded codebooks to compose
the encrypted messages by hand (authority: my own Army experience in the
|Top-secret IBM relay calculator (left) connected to IBM 405
The sequence in the film is accurate except in two respects. First, the
message would not have arrived on the Radiotype in clear text
(image 2), but rather as a nonsensical garble of characters; that is,
in code — which is why it had to be transcribed onto cards and fed
into another machine to be interpreted. Second, the 405 (which is really
not much more than a big card-driven adding machine) would have been merely
an I/O device for a decoding machine, such as the still little-known
nameless top-secret relay calculator shown at left and built by IBM for the
US Army Signal Corps, which is described in some detail in the Pugh book
below), which is also the source for the
image (thanks again to Henry for scanning it). Another possibility would
have been the SIGCUM
, a smaller (portable, even)
mechanical device, but I don't see any evidence of it being hooked up with
any punch-card machines.
|Type 040 tape to card punch|
From the descriptions below
, it would seem that
the same setup could be used for decrypting friendly messages for which the
key is known by simply swapping in some different plugboards. Also note
that the transcription from paper to punched cards would not be necessary if
the incoming message was directed to the Radiotype's paper tape punch, and
then the tape was converted to cards automatically; for example, by
Type 040 Tape Controlled Card Punch
. Then the cards could be printed
without any possibility of errors in the transcription, which would wreck
the decryption. IBM notes (on the page just cited) that "Signal Corps and
other military organizations used the IBM 40, and its counterpart IBM 57
card-to-tape punch, for defense work during World War II."
|Image: US Navy
If you think about it, it takes a great deal of skill and concentration to
transcribe encrypted text. Touch typists go fast because their fingers
"know" common patterns like T-H-E and I-N-G. But ciphertext is a string of
random characters with no patterns. Yet both my parents did this during the
war, all day, every day; it was their job at Navy Department headquarters in
Washington DC; they transcribed incoming Morse code to paper on big old
clunky manual typewriters and then handed the messages off to the decoders,
who worked in
. They also sent
ciphertext in Morse code. Both ways at
120wpm. That's all I know; they never talked about the details and it's too
late now to ask them. Reference 6
, however, has a
whole chapter on their workplace.
- The film Air
Force (1943), Wikipedia, accessed 29 May 2019.
and a Prayer, a 1944 film. It includes an almost identical
sequence: incoming Radiotype message taken
to an IBM 032 operator in the "decoding"
department, who punches it onto cards which are then fed to the 405,
decoded, and printed, but of course the decoding part is not shown.
- Interconnected Punched Card Equipment. Steve
Dunwell, who designed the secret relay calculator, was also the one who
engineered Wallace Eckert's groundbreaking switch
box at Columbia in 1934; this was the first instance of automated scientific
- Pugh, Emerson W., Building IBM: Shaping an
Industry and its Technology, The MIT Press (1995).
Radiotype: p.95. Deciphering enemy codes: pp.98-106 (figure caption, p.102:
"A relay calculator specially built for cryptographic work by IBM is shown
attached to an IBM Type 405 Alphabetic Accounting Machine."
[Steve "Red"] Dunwell's solution [to the inefficiency of using standard IBM
tabulators that generally operated at 150 cards per minute, to test
thousands of keys against a ciphertext] was to obtain a specially designed
processor built with electromechanical relays ... A unique feature of the
equipment specified by Dunwell and built by IBM was the function of its many
plugboards [seen in photo as rectangular enclosures on the face]. These
permitted the machine to be wired to recognize the sets of code-book units
that corresponded to the most frequently used words and to supply their
probabilities. Cards were fed into the machine [i.e. into the attached IBM
405] so that each card that contained part of an encrypted message was
followed by one or more cards with a hypothesized key. For each key the
machine performed the decryption, assigned probabilities to the resultant
words, and calculated the probability that the message segment had been
correctly decrypted. The relays were fast enough that the entire analysis
could be done between the reading of one card and the next — at the
rate of 150 cards per minute. The first unit worked exceptionally well, and
more units were put in service.
W. Dunwell, IBM Builders Reference Room, IBM Archives (Page 2),
the text of "World War II Code-Breaking Exploits Unveiled By Retired IBM
Engineer After 50 Years Of Secrecy," an IBM Europe/Middle East/Africa
Corporation press release distributed on February 12, 1992:
Stephen Dunwell, 78, waited 50 years to go public with selected information
on the black art of how a small team of engineers "hotrodded" commercial IBM
punch card machines with special relay calculators. Using data processing
techniques, they were able to obtain from machines running at a speed of 150
cards a minute the equivalent of more than one million comparisons each
second -- an astonishing feat unheard of, in public, until now ...
Within days of being tapped to be technical director of the machine branch
of the new U.S. cryptographic center, Dunwell found himself out of IBM and
in the Army with a gun strapped to his waist, and unlimited funding and
resources. Between round-the-clock efforts to adapt punch card-fed relay
computers to new uses, Dunwell found time to woo and marry a former school
teacher who became the secretary of the cryptographic center's
Commandant. "We fitted our honeymoon into a working trip," he says. "By
1943, the machine was designed, built, and working."
Dunwell, IEEE Computer Society Computer Pioneers by J.A.N. Lee (1992)
"During World War II he received a direct commission to the Army Security
Agency, whose mission was cryptography and code-breaking, using IBM machines
with attached relay calculators. He received the Legion of Merit for this
work, and returned to IBM at the end of World War II with the rank of
Interview with Stephen Dunwell, OH 153, Conducted by William Asprey,
Charles Babbage Institute, Center for the History of Information
Processing, University of Minnesota, Minneapolis, 13 February 1989:
[In] 1938 I was asked to come down to New York to what was then called [IBM]
World Headquarters ... At that time they broke the organization up and I
came back to the [IBM] Laboratory and worked on the thing that was called
"radio-type." I don't think many people realize that before World War II
IBM had a radio-operated typewriter that they actually sold to the services.
I stayed there until the advent of World War II ... the Signal Corps came to IBM and said they'd like to interview several
people for possibly going into the cryptographic operation, which was then
down in Washington, and later went
to Arlington Hall
station ... There were two general ways of approaching the cryptographic
machinery problems. One of these was
[the bombe, like
which was basically
machine in reverse, with spinning things] and the other used
punched-card equipment. We came out about on a par with the [bombe]. If
anything, our punched-card equipment came out better ... In the course of
all of that, I had gone to IBM and arranged for some array processing
equipment to be provided for us ... which would allow us to read a punched
card and punch back [or print] the decrypted result in the same card ... I
had [at Arlington Hall] 14 punched-card machines [meaning an IBM 405 coupled
to the special relay calculator] built by IBM that would read a card and
punch the result back in the card with the computation being made as an
array computation in a very short space of time with relays."
also Served, an album of IBM Special Products, Volume 1;
With the U.S. entry into World War II, the Signal Corps ordered quantities
of the Radiotype machines to equip its stations in San Francisco,
Honolulu, Panama, Puerto Rico and elsewhere, forming the Army Command and
Administrative Network (ACAN, see map).
Long-distance transmissions, e.g. from a ship in the western Pacific to
Washington DC would be done in relays.
Radiotype installations in New York, Dayton, Omaha, Seattle
were linked to the US Signal Corps communications
headquarters and its central radio station WAR in the Pentagon. These
various stations handled a wartime peak of 50 million words a day.
- Mundy, Liza, Code Girls, Hachette Books (2017).
An in-depth look at World War II military codebreaking.
Wikipedia, accessed 31 May 2019.
- Thompson, George Raynor, et al, The Signal Corps: the test (December
1941 to July 1943), Center of Military History, United States Army
(2003), Chapter VIII: "Signal Equipment: Wire and Radio". The IBM Radiotype
used a unique 6-bit code, not the common
(Teletype) code. It could transmit and receive up to 100 words per minute
— slightly slower than the fastest touch-typer. It was a stopgap
solution used until a more general all-purpose Radio-Teletype (RTTY) network
was developed that would have built-in end-to-end encryption and decryption,
but this took years and years so the Radiotype was used throughout the war
(as were, indeed, Morse code transmission... and carrier pigeons!).
Wireless Data Transmission, IBM 100 (IBM 100th anniversary material).