The Colossus Rebuild Project by Tony Sale

Colossus Reborn

The K Rack , its Switch Panel and Plug Panel

The large switch panel on the K rack in the centre of the picture, is where the code breaking algorithms are set up to enable Colossus to find the wheel start positions used on an intercepted Lorenz cipher message.

The algorithms are described in the wartime Albert Small report and in the history of the Newmanry. Both of these can be downloaded from

The complete operation of the panel can be explored in Virtual Colossus also available through codesandciphers.

This switch panel is not at present connected into Colossus but is wired up ready for connection.

The sloping panel in front of the K rack was introduced to avoid the operators having to go round to the back of Colossus to set up the Chi wheel patterns.

The patterns are plugged up on this panel by inserting Post Office shorting plugs into the rows of jack sockets. Two patterns can be plugged for each of the five K wheels. The patterns are selected by the switches at the bottom of the sloping panel.

This panel is also wired up but not yet connected into Colossus.

The large jack field on the relay rack on the left, was where the ring start positions could be plugged.

This page was originally created by the late Tony Sale, the original curator of the Bletchley Park Museum, and Secretary of the Bletchley Park Heritage Society.