MLAT Tracking

What signal is MLAT using for it’s calculations if the aircraft is not transmitting it’s position via ADS-B? For example, military aircraft don’t typically use ADS-B in my area but I sometimes catch them using MLAT. Is it just their mode-c/s transponder?

It just uses Mode A/C and fixed(or known) locations of multiple receivers.

That’s what I thought. Thanks!