This episode traces the blockade runner, a ship built to slip through a naval barricade rather than fight it, across more than two thousand years. In the Peloponnesian War, Leon of Salamis sent runners to Athens for reinforcements, and during the Punic Wars runners rowing at night with muffled oarlocks kept Carthage fed. In the 14th century the Victual Brothers ran provisions into Stockholm under siege by Queen Margaret I of Denmark. The core trade-off never changed: give up armor and survivability for speed and stealth.

In the American Civil War, the Union’s Anaconda Plan stretched about 500 ships across 3,500 miles of coast, roughly one per seven miles, so runners only had to beat the ships at the choke points. British investors, hit by the Lancashire cotton famine, financed long, narrow, shallow-draft steamers staged from the Bahamas and Bermuda, and historians estimate the cargo they delivered lengthened the war by up to two years. The episode follows the idea forward to German cargo submarines, a zeppelin sent toward Africa, Axis submarine runs to Japan, British motor gunboats in the Skagerrak, and modern narco subs.

• Civil War runners burned nearly smokeless anthracite, were painted gray, and could lower their smokestacks.
• The CSS Advance made more than 20 runs through the blockade before it was captured.
• The Union took more than 1,100 runners and destroyed another 355.
• The German cargo submarine Deutschland crossed the Atlantic and surfaced in Baltimore in 1916.
• In World War II, only 16 of 32 German surface runners sent to Japan made it.