Did Indy really travel hundreds of miles clinging to the side of the Nazi submarine? BONUS QUESTION: Does Belloq really swallow a fly?
BEST EXPLANATION: This happens right after the freighter transporting Indy and Marion is boarded by a crew from a German submarine. A few moments later, we see Indy scrambling on the sub’s deck—right before the captain gives the order to dive. So how does Dr. Jones survive this long underwater journey?
Turns out, history is on Indy’s side. Most subs of the time ran primarily on their diesel engines, meaning they traveled on the surface—or just below it—allowing the combustion engines to draw in the necessary air. (The subs would run fully submerged for short periods using battery power.) Assuming the sub had an incident-free trip, Indy could have arrived safely, albeit wet, cold and hungry.
As for Belloq swallowing that bug: You decide.