>In English, the pronunciation of ⟨h⟩ as /h/ can be analyzed as a voiceless vowel. That is, when the phoneme /h/ precedes a vowel, /h/ may be realized as a voiceless version of the subsequent vowel. For example the word ⟨hit⟩, /hɪt/ is realized as [ɪ̥ɪt]
For words beginning with h and where the first syllable is unstressed (historic, hypothesis, but not hitter, happy) it can be appropriate to use "an" rather than "a" as the associated indefinite article.
"an historic" sounds to me like "anhistoric" (as in "lacking history" kind of like "amoral")
I say "a historic" and "ahistoric" differently, I think. The first with a hard 'h' and a slight pause between words. The second with soft/no 'h' and no pause. If I heard somebody say "anhistoric" (soft 'h', no pause), I'd think they meant "ahistoric" not "an historic". Of course, context probably makes it clear regardless.
Growing up in DC with Scottish parents was always fun. Rolled Rs, different "wh" sound (Scottish English: wheels vs US English: weels) (noticeable expulsion of air on the 'wh' sound).
Mary (lady), merry (happy), marry (get hitched) all should sound different to me, but in MidAtlantic English they're often the same. Same for Kerrie vs Carrie.
In Ancient Greek polytonic orthography, vowels can have one of two diacritic marks: οξεία and δασεία. The second one is used to denote the /h/ sound (rough breathing). Words starting with vowels with this mark in their translation to English added the H before the vowel to denote this sound because of the lack of diacritic marks/accents