"Why were 15 British sailors sitting in dinghies?
How could they become surrounded by Iranian vessels?
Where was their mother ship and why would they allow the Iranians to leave with the sailors?"
Poor military planning.
Lack of cover and backup for boarding parties and their vessels.
Lack of existing standing orders REQUIRING the senior on-scene commander to protect his folks in whatever manner necessary.
Lack of a reaction plan to prevent enemy access to their port facilities after commiting this kind of aggression by destruction of those facilities if necessary.
Inexcusable lack of planning on the part of military leadership, especially since this exact same thing has happened before in the same waters.
I'd say that nails it square on...
lessons unlearned.
jw