Well, my main question was mostly _why_ it doesn't work (I may not have worded that very well). That said, presuming there was a way to make it work, I'd have i

Well, my main question was mostly _why_ it doesn't work (I may not have worded that very well). That said, presuming there was a way to make it work, I'd have it transmit all the available information about what's happening on the sub (respecting any technical limits). Then if the transponder stops sending data, you know something is wrong. Even if you don't know the exact location, knowing the last depth/speed the sub was at before losing comms, for example, is valuable. The caveat to all this is, like other comments said, radio doesn't work so well in salt water (which I didn't know).