I know in the update/addon we all are waiting for there will be more details given on incoming torpedos. But I have been sunk a few times not knowing I had an inbound torpedo whilst using the Periscope.
Having a sounding bell would be good, or a crewmen verbally informing you of it. The latter would be better i think.
I've already rambled on about crewmen voices and how it would increase atmosphere of being onboard a sub or ship in another posting so I won't go on about it.
But here's hoping it will be one of the new features in the addon-

