Most likely, a submarine would surface and render aid. This picture shows an Oscar class submarine rescuing some sailors in the White Sea.
However, the problem is that a submarine has limited capabilities to effect a rescue – no helicopter, and probably only small inflatable craft. Imagine this submarine attempting to wallow up to a freighter that is dead in the water in pounding seas – it ain’t gonna happen! Too much danger to personnel and the submarine itself.
Better to use its communication capabilities to alert other rescue platforms.
