200mm=8 inch. Never heard the 8 inch called anything else.
The last “large” howitzer was the M110. Technically it was 203mm but was referred to as 8”. That hasn’t been in use since the mid 1990s. The vast majority of armament used by the DoD is now referred to in metric.
An 8” howitzer is 203mm.
At least the M110A2 guns of the bn I was in were 😉.
I was in bn FDC, it was all manual; charts and darts, charge sticks and firing tables, a record of fire sheet and a field phone to the battery on a field desk, sitting under canvas and camo nets, the FDO sitting under a grease penciled standard of fire chart, with a stop watch around his neck... dang if I don’t bmiss it still 35 years later, sniff!