Colossus computer

The invention: The first all-electronic calculating device, the Colossus
computer was built to decipher German military codes
during World War II.
The people behind the invention:
Thomas H. Flowers, an electronics expert
Max H. A. Newman (1897-1984), a mathematician
Alan Mathison Turing (1912-1954), a mathematician
C. E. Wynn-Williams, a member of the Telecommunications
Research Establishment
An Undercover Operation
In 1939, during World War II (1939-1945), a team of scientists,
mathematicians, and engineers met at Bletchley Park, outside London,
to discuss the development of machines that would break the
secret code used in Nazi military communications. The Germans
were using a machine called “Enigma” to communicate in code between
headquarters and field units. Polish scientists, however, had
been able to examine a German Enigma and between 1928 and 1938
were able to break the codes by using electromechanical codebreaking
machines called “bombas.” In 1938, the Germans made the
Enigma more complicated, and the Polish were no longer able to
break the codes. In 1939, the Polish machines and codebreaking
knowledge passed to the British.
Alan Mathison Turing was one of the mathematicians gathered
at Bletchley Park to work on codebreaking machines. Turing was
one of the first people to conceive of the universality of digital computers.
He first mentioned the “Turing machine” in 1936 in an article
published in the Proceedings of the London Mathematical Society.
The Turing machine, a hypothetical device that can solve any
problem that involves mathematical computation, is not restricted
to only one task—hence the universality feature.
Turing suggested an improvement to the Bletchley codebreaking
machine, the “Bombe,” which had been modeled on the Polish bomba. This improvement increased the computing power of the
machine. The new codebreaking machine replaced the tedious
method of decoding by hand, which in addition to being slow,
was ineffective in dealing with complicated encryptions that were
changed daily.
Building a Better Mousetrap
The Bombe was very useful. In 1942, when the Germans started
using a more sophisticated cipher machine known as the “Fish,”
Max H. A. Newman, who was in charge of one subunit at Bletchley
Park, believed that an automated device could be designed to break
the codes produced by the Fish. Thomas H. Flowers, who was in
charge of a switching group at the Post Office Research Station at
Dollis Hill, had been approached to build a special-purpose electromechanical
device for Bletchley Park in 1941. The device was not
useful, and Flowers was assigned to other problems.
Flowers began to work closely with Turing, Newman, and C. E.
Wynn-Williams of the Telecommunications Research Establishment
(TRE) to develop a machine that could break the Fish codes. The
Dollis Hill team worked on the tape driving and reading problems,
and Wynn-Williams’s team at TRE worked on electronic counters
and the necessary circuitry. Their efforts produced the “Heath Robinson,”
which could read two thousand characters per second. The
Heath Robinson used vacuum tubes, an uncommon component in
the early 1940’s. The vacuum tubes performed more reliably and
rapidly than the relays that had been used for counters. Heath Robinson
and the companion machines proved that high-speed electronic
devices could successfully do cryptoanalytic work (solve decoding
problems).
Entirely automatic in operation once started, the Heath Robinson
was put together at Bletchley Park in the spring of 1943. The Heath
Robinson became obsolete for codebreaking shortly after it was put
into use, so work began on a bigger, faster, and more powerful machine:
the Colossus.
Flowers led the team that designed and built the Colossus in
eleven months at Dollis Hill. The first Colossus (Mark I) was a bigger,
faster version of the Heath Robinson and read about five thousand characters per second. Colossus had approximately fifteen
hundred vacuum tubes, which was the largest number that had
ever been used at that time. Although Turing and Wynn-Williams
were not directly involved with the design of the Colossus, their
previous work on the Heath Robinson was crucial to the project,
since the first Colossus was based on the Heath Robinson.
Colossus became operational at Bletchley Park in December,
1943, and Flowers made arrangements for the manufacture of its
components in case other machines were required. The request for
additional machines came in March, 1944. The second Colossus, the
Mark II, was extensively redesigned and was able to read twentyfive
thousand characters per second because it was capable of performing
parallel operations (carrying out several different operations
at once, instead of one at a time); it also had a short-term
memory. The Mark II went into operation on June 1, 1944. More
machines were made, each with further modifications, until there
were ten. The Colossus machines were special-purpose, programcontrolled
electronic digital computers, the only known electronic
programmable computers in existence in 1944. The use of electronics
allowed for a tremendous increase in the internal speed of the
machine.
Impact
The Colossus machines gave Britain the best codebreaking machines
of World War II and provided information that was crucial
for the Allied victory. The information decoded by Colossus, the actual
messages, and their influence on military decisions would remain
classified for decades after the war.
The later work of several of the people involved with the Bletchley
Park projects was important in British computer development
after the war. Newman’s and Turing’s postwar careers were closely
tied to emerging computer advances. Newman, who was interested
in the impact of computers on mathematics, received a grant from
the Royal Society in 1946 to establish a calculating machine laboratory
at Manchester University. He was also involved with postwar
computer growth in Britain.
Several other members of the Bletchley Park team, including Turing, joined Newman at Manchester in 1948. Before going to Manchester
University, however, Turing joined Britain’s National Physical
Laboratory (NPL). At NPL, Turing worked on an advanced
computer known as the Pilot Automatic Computing Engine (Pilot
ACE). While at NPL, Turing proposed the concept of a stored program,
which was a controversial but extremely important idea in
computing. A“stored” program is one that remains in residence inside
the computer, making it possible for a particular program and
data to be fed through an input device simultaneously. (The Heath
Robinson and Colossus machines were limited by utilizing separate
input tapes, one for the program and one for the data to be analyzed.)
Turing was among the first to explain the stored-program
concept in print. He was also among the first to imagine how subroutines
could be included in a program. (Asubroutine allows separate
tasks within a large program to be done in distinct modules; in
effect, it is a detour within a program. After the completion of the
subroutine, the main program takes control again.)