Populate numbers/letters in long list...???

Hello - I often need to populate long lists in excel and would like to know if there is any way to this in cells using numbers/characters/letters? For example... I have a cell filled with "U02_01P" and I would like to fill down remaining cells changing the numbers before "P" to the next sequential number ("U02_02P, U02_03P....). Is there an easy way to do this?? I'm not an excel expert - so an

y help would be appreciated!