if im not mistaken this stuff happens all the time. i know that during the coldwar and possibly up until a few years ago our subs were playing cat and mouse with the russians under the arctic ice 24/7
i watched this thing on tv about how during WWII destroyers and subs used to pass each other all the time and not know it. in one incident an american destroyer came so close to a sub without either noticing, that they both couldnt fire their weapons due to the range, and the men on the destroyer started throwing potatoes at the sub when it surfaced. the men on the sub started freaking out thinking they were grenades.