Guess it depends on who you are fighting and what tank/submarine you are in compared to the enemy.
If a sub gets caught it's game up pretty much, although modern subs are ultra quiet, although the Chinese ones are supposedly a bit noisy.
Tanks with active protection, blow out panels etc are quite survivable, especially with infantry support.
In a sub the potential for a pretty slow death and burning alive/radiation.
In a tank your more likely to die pretty quick with modern blow off panels and diesel engines cutting out the burning,well time for you to exit anyway.