What military aircraft do you get in your logs ?

[malc41]

Tom

As Dave says it depends on your proximity to the Mode S ground radar. Where you are you are literally surrounded by them.

[DaveReid]

I hardly ever get a mil ac NOT transmitting alt. I get AAC and RAF helis around here at 250' to 1500' always transmitting alt and I have NEVER had a US Mil ac not transmitting alt. That includes F-15s at LN.

Yes, I'd expect the Debden Mode S radar to see low-level traffic over much of East Anglia. 

Bear in mind also that if an aircraft drops below or beyond radar coverage, the altitude shown on BaseStation/RadarBox doesn't disappear, it just stays at the last known value.