This morning my mother sent me an email wondering if I knew why there was a "w" in the word "two." I did a little looking into the etymology of the word and discovered that it comes from the Middle and Old English word "twa," which is the feminine form of the word "twegen." Each of those words, as far as we know, were pronounced like they're spelled, with the consonantal "w."
I thought about it for a while and came up with a couple of theories, but neither really amounts to anything more than a guess on my part. The first is that it might have something to do with the influence of Norman French on the English language. But that one seems like a bit of a stretch, especially since Merriam-Webster's says that "two" first appears "before the 12th century," putting it potentially before or very near the same time of the Norman conquest of England in the 11th century. That doesn't seem enough time.
The other thought I had is that the pronunciation of the consonant "w" is actually not all that different from the vowel "oo"--the shape of the mouth between the two sounds is pretty close, to the point where if you slow down a "w" word, it typically becomes an "oo." So, maybe "two" was originally pronounced like "twoh," and due to natural shifts in the language the final "o" was dropped. And, since written language tends to change more slowly than spoken language, the spelling simply hasn't caught up yet.
Is this anywhere near the correct answer?
First, welcome.
While I haven't researched the word two specifically, I think your second theory, phonetic assimilation into the rounded vowel, sounds quite likely to me. If so, it would be very similar to what happened to the w sound in wh- (formerly hw-) words before rounded vowel sounds, e.g. who, whole, whose. The same such words before an unrounded vowel lost the h sound instead (for most English dialects), e.g. what, where, when, why, which, whale, whine.
I don't think you will find that two was ever actually spelled with -oo, but the pronunciation did shift to that sound.
The theory of phonetic assimilation would also fit nicely with the observation that related words with unrounded vowels were able to keep the w sound intact: e.g. twin, twain, twine, between, twelve, twenty.
Anyone know how two is pronounced in Wales, where you can find someone playing a crwth in a cwm?
No, but I'll point out that the 'w' is present not just in middle English but in Scottish as recent as Robert Burns ("twa"), in German (zwei), in Italian (due), Dutch (twee), Portuguese (dois—I know it doesn't look like a 'w', but it's a 'w' sound), Swedish (tvÃ¥), Latin (duo), Greek (δÏο) and probably many more, at least in the Indo-European languages. It's clear to me that the 'w' sound was originally part of the word, and was lost in a few of them: in English pronunciation (though not its spelling), in Spanish and French at least, probably a few others.[Later:] Also Russian (два, transliterates to "dva").
To Bob, I would add that AFAIK (at least in Swedish and German), there is no sound that is similar to the English "w" sound in "way" or "wow".
So, you do see the W in German spellings, but the pronunciation is always analogous to V sound in English, so the W and the V in "Wernher von Braun" is actually the same consonant.
So if the silent W is due to Germanic origins, and if it ever was pronounced, then it is more likely to have been closer to a V sound than a W sound.