submarines are not spaceships and are built to withstand external pressure not internal pressure
ravens are great vs water but may require targets to be spotted first by sonar.
you are correct that a fork will withstand temprature < 100c the vapor point of water all the way up to 1500c where they start get shake with fear
but perhaps the submarine contains gas (unless it has no internal atmosphere)
when gasses are heated they expand and given the water is boiling and likley not providing an opposing force the submarines may be experiencing forces they are not designed to contain
of course this would all make allot more sense if huge clouds of steam bellowed out from the napalm hitting water
hydrothermal vents on earth are about 350 celcius and are concidered dangerous
submarines have internal fire fighting capabilites but never the less fires are a big problem in contained inviroments as the heat has nowhere to escape so depending on the fuel and presence of oxygen fires can quickly reach the flashpoint of steel.. you also cant just spray water on the fire for too long or you will fill the vesel with superheated steam
and since steam is invisible (unless its deconpressing or condensing) but can still kill the crew in 3 horrific ways (drown , burn and crush) its very dangerous
