ERNIE II (Electronic Random Number Indicating Equipment), 1973, for generation of Premium Bonds Numbers, manufactured by Plessey.

Since 1st June 1957, a machine named ERNIE (electronic random number indicator equipment) has been used to produce winning premium bonds numbers. Premium bonds are a savings account where you can save and withdraw money and the interest is decided by a monthly prize draw. Each bond has an equal chance of winning, so the more you own, the higher your chances.

The job of routinely generating random numbers against bond holder’s numbers was far too labour and time intensive to be done by hand, so it was decided a machine would be built. Following on from their incredible advancements during the Second World War, this task was given to the codebreaking team at Bletchley Park who deployed similar engineering experience to their wartime activities. Both Tommy Flowers and Harry Fensom, who had designed and worked on Colossus worked on the project.

This machine is ERNIE II, the second iteration. By the end of ERNIE I’s life in early 1973, it was taking nearly 10 working days to generate winning numbers. This ERNIE drastically reduced the time taken to complete the draw and was over 30x quicker. ERNIE II used similar technology to the original where sensors counted the number of electrons passing through a diode at various intervals.

ERNIE II was active between February 1973 and August 1988. It generated 22,740,704 winning numbers which was a total value of £1,494,420,100.

ERNIE 5 is currently used to calculate premium bond numbers today but instead of using thermal noise to generate random numbers, it now uses light. Over 400 million winning numbers have been created by the various iterations of ERNIE, with nearly £20 billion in prizes given out.