I think that
Sauron took off
the One Ring himself and placed it in a safe place as he did not need to actively control the Elven Rings while he was in
Numenor and was able to access his native power sufficiently to be more that strong enough to achieve his goals.
Interesting reasoning, but personally I'm not quite convinced of it yet.
For example, why would Sauron take off his ring and leave it in
Barad-dur? That would only make sense if he was afraid that the Numenorians would take
the Ring from him. But first, they didn't know about
the Rings of Power, and second, I believe that Sauron was able to make the Ring invisible to others, just as
Galadriel, for example, was able to hide Nenya from others, at least from mortals. Furthermore, he should have feared that the Numenorians would plunder and destroy Barad-dur. And finally, he also needed the Ring on Numenor to exert control over
the Nine.
That would basically be like me taking a three-week vacation in New Zealand and leaving my smartphone and laptop at home while my door lock is broken.
And I actually would need the smartphone to plan my trip, book tickets and research information more quickly...
So I'd rather think that he had the Ring with him in Numenor, although of course it's a kind of plot hole how the Ring could come back again. As suggested in an older post, perhaps he could have influenced the ocean current in spirit form, so that his former, rotten Annatar-body, to which the Ring was still attached, was washed to
Middle-earth. Or his spirit could exert control over lower (sea) beings, like a kind of possession as with the
wargs or the wights, that were also controlled by
evil spirits...
In any case, it would be plausible that he could wield more power in spirit form than in
the Third Age, since the Ring remained on his destroyed body after Numenor's demise and he therefore knew exactly where it was.
He naturally had the One Ring, and so very soon dominated the minds and wills of most of the
Númenóreans.
Incidentally, I find this statement of
Tolkien's particularly interesting, since nowhere else is it said that the Ring is also capable of manipulating the minds of beings who do not themselves wear a (lesser) Ring.
I explain it as Sauron being able to boost his naturally innate abilities just by wearing the Ring.
This would also fit the concept of increasing power through externalization while at the same time risking loss of control.
Morgoth has in principle done something similar by shifting more and more of his own power into his
creatures and pseudo-creations...
