I've noticed that the "U" in Japanese is often silent. For example, Kiritsuke is pronounced "Kiritske", and Konosuke is pronounced "Konoske".
I'm wondering whether the "U" is always silent. Would Kanetsune be pronounced "Kanetsne"? The rule must be more complex than just "don't speak the U". Otherwise, words such as Usuba would be pronounced "Sba", which seems unlikely…
If you're speaking regular English, just pronounce it how it's spelled. You won't look stupid to most people if you pronounce the letters or if you copy people who seem to know what they're doing because most people do not speak Japanese.
If you want to say Japanese words as a native speaker of Japanese would say them, as if you were speaking in italics, as people often do when they have some knowledge of the pronunciation of a foreign language (i.e., with French or Spanish, which I hear all the effing time), then it's a little more complicated. I'll leave you with two rules in jargon and then try to break them down:
1) High vowels in Japanese are devoiced when they occur between voiceless consonants or at the end of a word.
The high (position of the tongue) vowels in Japanese are /i/ and /u/ (pronounced about like the vowels in "leak" and "Luke," respectively). A voiced vs. voiceless consonant is just as you might guess from the name. There are consonants in all languages that can't be pronounced without some vibration of the vocal chords. Many of these consonants have a voiceless version. For example, /b/ is voiced but /p/, which is pronounced with the lips in exactly the same position, is voiceless. You could view /b/ as otherwise the same consonant as /p/ except for lack of voicing. So in answer to your question "why isn't Usuba pronounced 'sba,'" because /b/ is voiced.
2) When <u> occurs after <o>, it represents a single sound, long /o/, and not a complex diphthong of two vowels.
Japanese,
unlike English (despite terminology that may be used imprecisely by lay people), differentiates between long and short vowels, i.e., in relative duration, which can cause words to mean totally different things. When Japanese is written in Roman letters, there are different ways to transcribe vowel length - it is often NOT indicated - but for reasons I have never researched, long /o/ is spelled in Japanese, and sometimes carried over into Romanization, as <ou>. The only place I see this mattering for pronunciation of words related to knives would be
kurouchi and maybe names of knife makers, although again, it's usually not represented in Romanization, and I'm not sure why it was preserved in
kurouchi. Basically, don't worry too much about this too much, but if you can remember that the <ou> in
kurouchi is a long /o/, then you will sound a bit more knowledgeable than the average knife enthusiast.