ATACMS Block 1 used GPS, phased out in 2009. Block 1A use both GPS + inertial guidance. Anything carrying a penetrator (think Kerch) is probably Block 3, GPS plus improved inertial guidance system. I think that improved system is in all the 1As as well. The real question is which versions are going (and have gone) to Ukraine. We've mostly been sending phased-out stuff, but if some of those are carrying penetrators...