"And when the tablet is shot out in battle, how do you call for help?"
Well, there are the maritime signal flags and the semaphore flags. Wuthering Heights and all that...
BTW, if the engine fails are the seamen equipped with oars? There's only so many reasonal backup systems. How often these ships need to rely on signal lamps?
"Sometimes there's a good reason to have someone with a bit of knowledge on the bridge, especially in the military."
Even a dummy like me with no interest in learning the Morse codes knows the SOS code.