Originally Posted by
Wensleydale
If the military aircraft does not turn on Mode S (or probably more usually leaves it in standby) then it will not show. There may be areas of airspace that require Mode S to be turned on - then you will see it. If the military aircraft sets emergency on its transponder, then the emergency is automatically sent on all modes - hence the emergency indication seen on Mode S from the F-35. At the end of the day, the presence on the screen for Mode S/squitter depends upon what the aircrew set on their transponder and their emission control instructions.
the hex codes are filtered between raw receipt from enthusiast receivers and retransmission. This is done out of a sense of responsibility by FR. however, there are a few, Voyager due to the PFI, and new aircraft that are the exception. If you scan the UK with adsbexchange with a filter selected to military, you will see plenty of tracks. View the same in FR24. Missing. They come from the same source data.
you can’t have mil air assets goofing around without mode S, it’s too much of a risk to civilian users.