Gyro Horizon Indicator, Mk IC, RAF, US Navy, NOS, Ref 6A/1649

Here is a WWII-era Gyro Horizon Indicator, aka Artificial Horizon, Mark IC, Stores Ref 6A/1649, made by Sperry in 1944 (part number 650412), as used across various aircraft of the British Royal Air Force.  It appears to be New Old Stock as the red protective paper disc over the vacuum filter is still in place.

Common to the British version is the lack of a caging knob, whose purpose is instead fulfilled by a caging screw on the bottom of the case which is uncaged upon installation. Also common to the British version is the stamped statement "Do Not Jar Handle Like Eggs".

What makes this indicator quite unique and possibly rare is the US Navy anchor symbol stamped on its side.  Our hypothesis is that this indicator was intended for an aircraft developed by the US Navy with modifications specifically for aircraft ordered from its manufacturer by the RAF or Royal Navy Air Force, such as the Grumman fighters Martlett (US F4F Wildcat) and Hellcat (US F6F), Vought Corsair I & II (US F4U Corsair), Grumman torpedo bomber Tarpon (US TBM Avenger), and others. 

It is in superb condition given its 1944 date of manufacture.  Measures ~4.5 inches diameter and 6.5 inches deep.