Does anyone know what the difference was in a battalion vs. a regiment, as in 7th Battalion MS Infantry vs. 7th Regiment MS Infantry? If I understand correctly, a battalion is usually part of a regiment, so why the difference in the WBTS?

This started off as a question about the 7th but I noticed there are several units that had the same number, just were different in battalion or regiment. Didn't that get cofusing at the time, as it often does now when someone only writes 7th MS and you have to do extra research to find out if its the Batt'n or the Regiment?

Thanks,
Lisa