I think in real life in a neutral port, that the first reaction would have been, "was this an accident?" Given that submarines and torpedoes are stealth weapons there may have been initial confusion as to whether this was a magazine detonation or sabotage.
Assuming they figure out it is a submarine attack and you get clean away, it's hard to gauge what the reaction would be. The US did not declare war after an U-boat sank the US destroyer
Reuben James, whilst she was escorting convoy HX 156. This was only weeks after the
USS Greer was fired upon by an U-boat in September of 1941 and the torpedoing of
USS Kearney on October 17, 1941. There might have been a diplomatic exchange between US and Germany and a subsequent increased diligence and reinforcement of the US Atlantic Fleet. On the German side, Admiral Raeder might inform his commanders that Hitler desires to avoid provoking the US at the moment, and to be more careful and circumspect.
That means you.