Here's a copy from a post last week!
1993: Original USP9 and .40.
1994: Reduced the slide weight by 1.1 oz.
1994-95: Change to a polygonal rifled barrel (Prior barrels were standard land and groove)
1994-95: Change trigger transfer bar.
1994-95: Change recoil guide rod to a "captured spring version".
1995: Change trigger mechanism.
1995-96: Add rubber spur to hammer.
1995-96: Change angle on slide lock.
2000: Add locking feature to hammer strut support.
2001: Converted captive recoil spring retainer from c-clip to machined end on USP Compacts.
1993: Original USP9 and .40.
1994: Reduced the slide weight by 1.1 oz.
1994-95: Change to a polygonal rifled barrel (Prior barrels were standard land and groove)
1994-95: Change trigger transfer bar.
1994-95: Change recoil guide rod to a "captured spring version".
1995: Change trigger mechanism.
1995-96: Add rubber spur to hammer.
1995-96: Change angle on slide lock.
2000: Add locking feature to hammer strut support.
2001: Converted captive recoil spring retainer from c-clip to machined end on USP Compacts.