Pretty much the usual way. Ensign Prozski reported for duty pale and sweating, and once they’d voted to defect and smashed the radio, it wasn’t like they could request a medevac. Within a couple days their little pressure chamber had yielded to the inevitable mathematics of infection.

Funny thing about nuclear subs: not only can they run silent and deep for decades, they can sneak in a mutation or two while doing so–even in viral DNA. Prozski and his comrades retain awareness and volition. They just get used to being a little peckish, speaking Russian, and cruising for amphibious sex.