When is w a vowel?

Answer

"W" is a vowel in the very few words borrowed from Welsh. Two of these are "cwm", which is a special type of valley, and "cwr", which is a type of train tracks made from single long rails rather than a bunch of short ones put together.

You can find more information on the links below.

Answer

The above is not the only way in which w is used as a vowel. W is also used in diphthongs at the end of words, ie., how, row, low, bow, etc. In these instances, it is serving the purpose of a vowel. The letters l, m, n, and r, can also be used in this manner, ie., bottle, bottom, button, and butter.

(see the related link)