On December 7, 1941, Japanese aircraft bombed the U.S. Naval fleet at Pearl Harbor from above. But what’s less well known is that the attack also came from underneath, by way of high-tech Japanese midget subs that slipped into the harbor before the aerial assault. Today, historian Parks Stephenson thinks he’s found the last of these subs—one that has been missing for almost 70 years.

(Originally produced for WGBH Radio News.)