Claudian letters were developed by, and named after, the Roman Emperor Claudius. . . . He introduced three new letters:

A backwards, upside-down “F” to represent consonantal U, possibly inspired by Greek Digamma. . . .

A broken “H” to represent the sound of Greek Upsilon. . . .

A backwards “C” to replace BS and PS, much like “X” stood in for CS and GS, and inspired by Greek Psi.

These letters were used to a small extent on public inscriptions dating from his reign but their use was abandoned after his death. . . .

However, later on, the letter Y was added, filling the role of his broken “H”. His first innovation [three new letters] would not catch on for over 1500 years, when U, V, and W became recognized as separate letters. (Until the 17th century, U and V were represented by the same letter, printed V as capital, v initially, and u medially and finally, resulting in spellings such as “haue” and “vpon”.)

—Wikipedia, the free online encyclopedia. I know it’s not authoritative, but no one else online has anything on this vital shit!