Originally Posted by
Jet Dragoneer
The transponder issue might be a red herring. I have a faint memory from my distant past...
They are fitted with and do use a regular civilian transponder. Unfortunately they typically turn it off when encroaching on an FIR and mastering the art of being a safety problem, but not always. They also tend to file regular flight plans for long-range transits (eg to Venezuela) and for these they squawk & talk normally.
You may be confusing military-only IFF systems and yes, there is little perceived need for these systems to cooperate!