In Australian English, calm rhymes with farm and uses a long vowel, while com uses a short vowel and would rhyme with prom. (I know this doesn't help much because some American accents also rhyme prom with farm).

Consider the way "Commonwealth Bank" is pronounced in this news story: https://youtube.com/watch?v=MhkuHGRAAbg. An Australian English speaker would consider (most) Americans to be saying something like "Carmenwealth" rather "Commonwealth". See also the pronunciation of dog vs father in https://www.goalsenglish.com/lessons/2020/5/4/australian-eng....

It really ruins some poetry.