“Dee-twenty” and “die-twenty” pronunciations

(I asked this question recently on reddit, and got a mixed assortment of not-quite answers.)

Most gamers pronounce, e.g., ‘d20’ as "dee-twenty", or ‘3d6’ as "three dee-six". But a certain contingent of (mainly older) gamers pronounce them "die-twenty" and "three die-six", respectively. Does anyone know when and where this nomenclature arose? My suspicion is that it comes from old-school wargaming, but I’m not certain. (I realize this is a little tangential to RPGs, but that’s the one topic I can think of that it is tangential to.)