It is very hard to open a door under water. The pressure of the water is too resistant. That's what under-water aerobics is all about! Even above water the doors of those vintage Oldsmobiles were heavy, heavy. I used to drive one, hauling 4 little kids to and from school, camp, scouts, etc. I couldn't believe the difference when I traded the Olds for a Ford station wagon. Easy peasy, by comparison.
“It is very hard to open a door under water.”
I found the text recap of an old “Mythbusters” episode.
“...the water pressure exerted against a sinking auto makes it extremely difficult to open a door and swim to safety.”
“...the water pressure differential between the inside and outside of the cabin was simply too great for Adam to pry open the driver’s side door.”
(How did Teddy get out?)
“But once the sinking sedan had filled to the brim, the pressure difference stabilized, allowing the door latch to release.”
http://www.discovery.com/tv-shows/mythbusters/mythbusters-database/open-the-door-of-a-sinking-car/
More mystery.