These chambers were used to conceal messages or objects. Toothpaste tubes were also used, but clearly the chamber would have been smaller. All the tubes were branded with the name of an appropriate manufacturer, and the top of the tube was filled with shaving cream or toothpaste so that it could be used normally, averting any suspicion.
If the concealed object, such as a code printed on silk, required damp proofing, it was placed inside a balloon. This would be placed in the tube along with a bit of cotton wool to keep it in place. Instead of messages, glass-frosting ointment was also sometimes hidden in this secret compartment. The ointment could be used for sabotaging optical instruments.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.