9. Type XXI U-boat

The Allies were fortunate that the Type XXI U-boat arrived too late to see combat. Had it been deployed before the end of war, it could have had a devastating impact on the Battle of the Atlantic. The Type XXI had numerous advanced features for its time, including high-capacity batteries that enabled it to remain underwater for days, a streamlined hull, and a snorkel to recharge the batteries while underwater. With an underwater speed of 17 knots, it could actually outrace most surface warships.