Let me throw out a couple of hypotheticals in relationship to this sinking:
- US Sub contacts a P-8 and it re-directs from its current mission to contact the Iranian vessel with the challenge to surrender.
- What potential risk is there of the P-8 abandoning it's current mission? They don't just fly around for fun.
- What is the risk to the P-8? Is the Iranian vessel going to surrender to a radio message only? An unidentified blip on their radar? Or will the P-8 need to get into visual range and display the fact it has weapons that could target the ship before they would be willing to surrender?
- Can the P-8 shadow the Iranian vessel all the way to the neutral port to ensure that it complies? Does the US sub have to continue to shadow them to make sure?
- Assuming that the Iranian ship surrenders is there the possibility that while enroute back to port that they figure out that a US Sub may have been who initially spotted them and sent the P-8 looking for them?
- If they determine there is a US sub in the vicinity is there any risk that the Iranians detect them and fire torpedoes at them?
- Both China and Russia are allies of Iran (being dependent on oil/drones). Is there the possibility that the Iranians send out a message that they have been detected? What if the Russians or Chinese have their own subs in the vicinity and decide to investigate the situation? If they happened to detect the US submarine could they pass that information on to the Iranian ship so they could possibly attack the sub?
- The Iranians have intentionally attacked civilian targets and oil infrastructure in order to cause economic damage. What if on the way back to port they come across a foreign tanker and decide to attack it in hopes of sinking it before the US can respond? Or damage the port facilities in Sri Lanka before scuttling themselves blocking the harbour?
The way I see it there are so many possibilities left open by leaving an enemy combatant with the potential to cause damage/chaos in a war. None of these possibilities are at all highly likely, but do you leave the opening there for them?
Whether you agree with the political decision to launch this war or not I think that once hostilities have started you have to act like you are at war and not give any openings to the enemy. During WWII one of the major reasons for the US victory against Japan was the unrestricted submarine warfare against enemy shipping. German U-boats almost did the same to the UK. I don't doubt that in the next major global conflict that it will be similar. I can definitely see Canadian ships and aircraft needing to take out oil tankers, etc. in order to starve China of fuel, etc.
Unfortunately war is not pretty. That's why we need to try so hard to avoid it.