What is the etymology of ‘A-OK’?

I know it became popular during Project Mercury. I’ve used voice-activated intercoms in aircraft, so I know that if a syllable isn’t uttered the first syllable of whatever you say will be clipped. (Which is why I prefer the set-up in the helicopters I’ve flown; where you have to push a button, or else switch to ‘always hot’ mode.)

Am I correct in assuming that the ‘A’ in ‘A-OK’ was originally a syllable to open the VOX circuit on a voice-activated intercom?

Certainly 1961 is when it became a national phenomenon in the public eye.

A May 1961 editorial noted that it was “engulfing our Nation as the mot”, but pointed out that in Alan Shepard’s Mercury flight, Shepard never used the term “A-OK” but rather said things like “all systems–GO” in response to questions from the ground. The paper noted that many newspapers and magazines had mischaracterized this. It further said that Col. Shorty Powers on the ground used the phrase in response to Shepard’s comments.

I can’t vouch for more that that.

I’ve seen suggestions that the ‘A’ means ‘All’, which would be redundant.

IME with voice-activated intercoms I found myself starting sentences with ‘Ah’; as in ‘Ah, Mount Shasta is awesome’, or ‘Ah, do you see the Beechcraft?’. Otherwise the person I was talking to would hear ‘…nt Shasta is awesome’ or ‘… you see the Beechcraft?’.