Maybe! Most of those unmanned narcosubs are cut-down speedboats hulls, to my knowledge. The truly watertight/submerged ones are few and far between; it's a lot of investment for marginal decrease in observability.

My money is still on low-observable attack craft, or a high-low mix that deprioritizes submersibles. Iran has an impressive panopoly but also has casus belli to lie out their nose. If Iran does have fully submersable UUVs, I'd expect them to be saved for a direct confrontation with the US Navy, not tankers.

I could definitely be wrong though, I don't have any insider info to work with here.

> Most of those unmanned narcosubs are cut-down speedboats hulls, to my knowledge.

Some are now fully submersible: https://insightcrime.org/news/under-radar-what-hundreds-ofna...

I think it is indeed more likely that they used a low-profile boat, but I won't discount a full submersible. Or maybe a combination: a low-profile boat that uses a regular outboard gas engine to get close to the target, and then dives and attacks like a torpedo.

> If Iran does have fully submersable UUVs, I'd expect them to be saved for a direct confrontation with the US Navy, not tankers.

I don't think they can do serious damage to large US Navy vessels.