A coded message

At the end of 1950, Christopher Hinton, the head of UK’s atomic factories, wrote to a Miss Lowrison, who I presume is personal secretary of Lord Portal, Hinton’s overlord in the Ministry of Supply. The very first of the nation’s military plutonium production reactors had just sputtered into life after experiencing half a year of difficulties, and everyone desperately hoped that reactor could now be boosted in power to a level where it could commence to manufacture enough plutonium in its innards for an atomic bomb test. Portal must be on holiday, for Hinton plans to send him a coded message to tell him when the reactor went “on power.” We might now think, in 2023, that this mania for secrecy was silly, but less than a year earlier, scientist Klaus Fuchs had been arrested as a Soviet spy on British soil.

I have your message about telling Lord Portal when the pile goes on power. I am asking the factory to send this message to his home address and to use the same code which they are employing to notify me. If the pile goes on power during the Christmas holiday he will therefore receive a messages which reads as follows:- ‚ÄúPlenty of Water Ehen River” Part of our water supply is pumped from the River Ehen which makes the message a reasonable one and the initials of the words speak for themselves.. Our objective is to get the pile up to 1 megawatt power by Friday night. It will then be shut down while the staff go on Christmas holiday; after Christmas a final, check up will be made on the internal fittings of the pile and then it will go back on to power during Christmas week and work up to full power by the end of January. Could you let Lord Portal know this?

Hinton, Christopher. 1950. Hinton to Lowrison, Dec. 20, 1950. AB 8/29. National Archives, Kew, United Kingdom
Hinton letter