Developed by Christopher Clayton Hutton at MI9 this is a flat bar type compass in a rounded diamond shape approximately 28mm in length. Luminous dots to indicate North and South. There is a hole at the centre to enable the user to tie the compass to a piece of thread. When hung in a glass of water the compass is steadied and will point North. These were intended to be hidden inside an airman's shirt collar or jacket lapels to provide a useful escape or evasion tool in enemy territory. Possibly not too practical given the compass is only stable in water! Two available, priced individually. Very good used condition. Stock code E21872/3.