This is a British RAF 1950s Mk. 4F Gyro-stabilised directional compass, as used on aeroplanes such as the De Havilland Vampire and Supermarine Swift. This sort of compass can be locked onto a bearing, which it then follows, which was very useful in the days before GPS for finding airports/targets. This item appears to be in serviceable condition.

A De Havilland Vampire

 This item is rare and unusual.