I'm gonna bet they didn't board the tanker, or as Iran said tried, got fired on and left.Isn't having US special forces board and seize tanker ships is super risky. Who is to say these Iranian tankers don't have secret pop-up MANPADS or ship-based SHORADs to blow up these incoming US helicopters or small boats? Who is the say these Iranian tankers aren't booby-traped like crazy or set-up with IRGC special forces onboard that can lay an ambush? This pushes it to Close quarter combat really equalizes the two militaries and reduces US airpower/firepower/tech advantage.
1 - Most obvious is they wouldn't need to target the engine room if they could board.
2 - Targeting the engine room make boarding meaningless as US has no ability to tow the ship anywhere, so they'd have to take a risk they wouldn't take prior to firing, but only after the reward for taking that risk went to zero.
3 - US claim they went onboard to inspect cargo, which is an obvious lie because you physically can't open containers at sea.
I'm gonna bet the only reason they claimed they boarded the ship after firing on it is because it's impossible to explain why they'd fire on a ship if they already boarded it.
But hey all they need to do is release a video of the boarding and standing on bridge, weird they didn't release any along with video of opening fire, but I say we wait 48 hours to make the call.