The comical bus that splashes into the river on a family vacation was once a critical piece of World War II military technology. This episode traces the history of the DUKW, known as the Duck, from a logistical problem no landing craft could solve: getting ammunition, food and reinforcements from ships anchored miles offshore directly to the front lines without stopping on a contested beach. It introduces the unlikely design team of yacht designer Rod Stephens Jr., British sailor Dennis Puleston and MIT engineer Frank W. Speir, and explains why the Army and Navy initially rejected a vehicle that fit neither bureaucracy.

The turning point came in 1942 near Provincetown, Massachusetts, when the experimental DUKW drove into a storm with 60-knot winds to rescue seven stranded Coast Guardsmen after conventional boats failed. The episode then bre ...