Horizon.

This AI is the earlier Mk1 type with the ‘skyview’. It’s been in for service and had some white paint gobbed on it, but you can still see some of the original gold foil. They were usually luminous too. They were of course also used in civil a/c pre-war from about 1936 onwards.

The Mk1A was this unit inverted, but the later devices used white paint for use with UV lights etc and the symbology was simplified too. Same basic unit however. I think the revised version started to come in around 1941.