Can a short vowel have the same letter twice and it is a vowel?

The vowel pair AA (from Dutch) is an umlaut A as it is usually paired with an R.

The vowel pair OO has short and long sounds (good, foot / cool, moon).

The vowel pair EE is almost always long E. (it sounds like a short I in been)

Two I's together (e.g. radii) are pronounced separately as a long E and long I.

The vowels U and Y are never double vowels.