In standard aviation phraseology it's "fife" for the number five and "niner" for the number nine, to avoid confusing between them.

ICAO standard prescribes "fower" as four (making it two syllables), as well as all the others that have been cited (tree/three, fife/five, niner/nine).

And „tree“ instead of „three“.

You sure that wasn't just an Irishman doing the countdown?

„The ICAO, NATO, and FAA use modifications of English digits as code words, with 3, 4, 5 and 9 being pronounced tree, fower (rhymes with lower), fife and niner. The digit 3 is specified as tree so that it is not pronounced sri; the long pronunciation of 4 (still found in some English dialects) keeps it somewhat distinct from for; 5 is pronounced with a second "f" because the normal pronunciation with a "v" is easily confused with "fire" (a command to shoot); and 9 has an extra syllable to keep it distinct from the German word nein "no". (Prior to 1956, three and five had been pronounced with the English consonants, but as two syllables.?“

https://en.m.wikipedia.org/wiki/NATO_phonetic_alphabet#Pronu...

Jamaican?

They used to say fiver instead, as well

That sounds even more like "fire"!

Is that meant to sound less like “fire”??

No, fiver is occasionally used by beginning aviation students though in confusion (DAMHIK).

I bet they didn't.

I am not claiming it was standard, only that it was used. You can hear it in old WWII footage.