Heath Robinson (codebreaking machine) facts for kids
The Heath Robinson was a special machine used by British codebreakers. They worked at Bletchley Park during World War II. Their job was to break secret codes. This machine helped them decrypt messages from a German teleprinter cipher machine. This German machine was called the Lorenz SZ40/42.
The codebreakers gave the Lorenz machine and its codes a nickname: "Tunny." They named different German teleprinter ciphers after fish. The Heath Robinson machine was mostly electro-mechanical. This means it used both electricity and moving parts. It had only a few valves. It was an early version of the electronic Colossus computer. The women who operated it, called Wrens, nicknamed it "Heath Robinson." This was after a cartoonist named William Heath Robinson. He drew very complex machines that did simple tasks.
Max Newman created the plans for what the machine needed to do. Frank Morrell from the Post Office Research Station designed most of the machine. His colleague, Tommy Flowers, designed a key part called the "Combining Unit." Dr. C. E. Wynn-Williams from the Telecommunications Research Establishment made the fast electronic counters. Building started in January 1943. The first machine arrived at Bletchley Park in June and was soon used to help read secret messages.
The Heath Robinson machine was a bit slow and sometimes broke down. So, it was later replaced by the Colossus computer. Colossus was used for many tasks, including breaking codes from the Lorenz SZ42 machine.
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How Heath Robinson Broke Codes
The Heath Robinson machine used a special method created by Bill Tutte. This method was called the "1+2 technique." It looked at the first two parts of each character in the secret message. It then combined these with parts of the secret key made by the Lorenz machine.
The machine used two long loops of paper tape. One tape had the secret message. The other tape had a part of the key. The key tape was made a bit longer than the message tape. This allowed the machine to try every possible starting position for the key. For each starting position, the machine counted how many times certain patterns matched. If the count was high enough, it was printed out. The highest count usually showed the correct starting position for the key. Once they found this, they could figure out other parts of the key. This helped them remove the key from the message. Then, human codebreakers in the Testery could work on the remaining message.
Moving the Tapes
The "bedstead" was a system of pulleys. It moved two continuous loops of paper tape at the same speed. At first, it used wheels with teeth to pull the tapes. But this damaged the tapes. So, they changed it to use friction rollers. The toothed wheels then just kept the tapes in sync. The machine could read up to 2000 characters per second for shorter tapes. For longer tapes, it was 1000 characters per second.
The tapes passed by special sensors called photo-electric cells. These cells read the holes punched in the tapes. The tapes could be from 2000 to 11,000 characters long.
Reading the Tapes
The machine read the holes in the tapes using light sensors. These sensors were placed very close to the wheels that moved the tapes. This helped reduce problems if the tapes stretched. Ten sensors read the message characters. One sensor read the sprocket holes that guided the tape. Two more sensors read special "stop" and "start" signals that were punched into the tape by hand.
The Combining Unit
Tommy Flowers designed the "Combining Unit." He worked at the Post Office Research Station. This unit used thermionic valves (also called vacuum tubes) to do its calculations. It used a type of logic called "Boolean "exclusive or" (XOR)." This is a way of combining two pieces of information.
Here's how XOR works:
| INPUT | OUTPUT | |
| A | B | A ⊕ B |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
In this table, 1 means "true" and 0 means "false." If the two inputs are different, the output is 1. If they are the same, the output is 0.
The combining unit used this logic to help with Tutte's statistical method. It compared the secret message tape with the key tape. It then counted how many times the output was 0. A high count meant there was a good chance that the key tape was in the correct starting position.
Counting the Results
Dr. Wynn-Williams designed the counting system for Heath Robinson. He had studied how to count tiny electrical signals. The counters he designed used special tubes called thyratrons. These tubes could switch between two states, like an on/off switch.
The counters on Heath Robinson used these tubes and relays (electrical switches) to count. They counted in groups of 1, 2, 4, 8, and larger numbers. After each run of the message tape, the machine compared the total count to a set number. If the count was higher, it was displayed. It also showed the position of the key tape. At first, the Wren operators had to write these numbers down. This often led to mistakes. So, a printer was soon added to print the results automatically.
Improving the Robinson Machine
The first Heath Robinson machine was a test version. It worked well, even with some problems. Most of these problems were fixed as they developed "Old Robinson." However, Tommy Flowers realized he could build a machine that made the key electronically. This would solve the biggest problem: keeping the two paper tapes perfectly in sync. This idea led to the creation of the Colossus computer.
Even after Colossus was successful, the Robinson machines were still useful for some tasks. Improved versions were made and given nicknames like Peter Robinson and Robinson and Cleaver. These names came from famous department stores in London. A later and even better machine was called Super Robinson or Super Rob. Tommy Flowers designed this one. It had four "bedsteads" to run four tapes at once. This allowed it to do more complex codebreaking tasks.
