That is, the Latin /u/, /ʊ/ and /w/ (all encased within Vv).
Latin script did not differentiate between V and U. Historically, V originally represented the sound of U, and F represented the sound of W (much like the the beloved digamma [ϝ] of Greek). All four of these sounds /u/ and /ʊ/, /f/ and /w/ existed in the Latin language over the entire historic period. The confusion arises from a change in script, not a change in speech.
So, /u/ and /ʊ/ were V and /w/ was F, but then F became /f/, so V also became /w/, resulting in V as /w/, /u/ and /ʊ/. The V was one letter with three phonetic powers: two vowels, and one consonant. To make matters more reasonable, but perhaps also more confusing, the consonant /w/ is considered a semi-vowel, glide or approximate. Must like the Latin I (where i operates as glide consonant /y/), the Latin V is always followed by a vowel, and is effective the ‘edge’ of the vowels syllabic unit.
Let’s look at some examples.
- Greetings, Julius Caesar = AVE IVLIVS CÆSAR = avē, Iūlius Caesar ~ /awe yuliʊs kʰαιzeɹ/
This example has pretty much everything we need to see. It shows all three uses of V = as a glide, attached to the long ē in avē, as a long ū and as a short u.
Note that that proper ‘u‘ can also approach the English w /w/: aqua, anguis, cōnsuētus [cf. quart, anguish, suave]
The Essential AG: 5n