In recent blogs we explored reasons why the German submarine attack that sank the British passenger ship Athenia in the first day of World War II is largely forgotten today. The facts that more than 90 percent of the ship’s passengers and crew survived, that the Nazi government denied responsibility for the attack, and that the death of 30 Americans aboard Athenia did not bring the U.S. into the war, were all seen as contributing to this historical oversight. In today’s blog we continue our exploration with a look at the rules of war.
Press accounts of the Sept. 3, 1939, attack all expressed shock that it had come “without warning.” Today such a reference sounds quaint and naïve, but in 1939 the rules of war – agreed to under international treaties – required submarines to warn certain prospective victims of their intention to attack.
During World War I, German submarines, or U-boats, proved to be such a devastating weapon that following the war, there was talk of outlawing submarines altogether. Negotiators ultimately agreed submarines could be retained as weapons of war so long as conditions were placed on their use.
These conditions were established in 1930 and reinforced in the 1936 London Submarine Protocol, which set out rules for the conduct of submarines in future wars. Enemy warships and merchant ships sailing under escort could be attacked without restriction. But submarines could not attack unarmed, unescorted merchant ships without first giving warning, and to do that they had to be on the ocean’s surface. Once a submarine stopped a merchant ship, it could send a boarding party onto the ship, and if any contraband was found in the ship’s hold, the ship could be sunk.
Submarines are most vulnerable while they are surfaced, so the protocol’s requirements were totally impractical from a tactical standpoint. Nevertheless, 35 nations, including Germany, signed the 1936 London Submarine Protocol. For the three years following its adoption, however, there had not been a major maritime conflict to test its effectiveness.
When Athenia was sunk by a U-boat without any warning, the world feared Germany was returning to the practice of unrestricted submarine warfare that it followed in World War I.
The Nazi U-boat captain who sank Athenia told his superiors he thought he had attacked a British armed merchant cruiser, a legitimate wartime target. He only discovered his mistake after coming to the surface to observe the sinking ship. Indeed, he continued his war patrol and sank two more British merchant ships while scrupulously following the protocol rules.
But by the end of September 1939, Hitler issued several conditions under which his U-boats could ignore the protocol’s restrictions and attack merchant ships without warning. These conditions applied if merchant ships were blacked out, used their radios to report German naval positions, or were obviously armed.
The practical effect of the Führer’s order was to sanction unrestricted U-boat warfare. Within a month, U-boat attacks on merchant ships without giving warning became commonplace, which prompted all others to abandon the London protocol. Once the world’s navies adopted the tactics of unrestricted submarine warfare, the shock of Athenia having been sunk without warning quickly faded.

Next month: War’s utter devastation