German or Austrian subway system, 1938 (originally in reference to Berlin), from German U-bahn, short for Untergrund-bahn, literally "underground railway."
When Did The Letter U Enter The Alphabet?There was no letter U in the alphabet. Well, that’s not the entire story. There was the sound for the letter we call U, but it didn’t look like U. It looked like V. The Classical Latin alphabet had only 23 letters, not the 26 that we have today. (This is why the W looks like a double V but is pronounced like a double …
Online Etymology Dictionary, © 2010 Douglas Harper