One hundred years ago, in October 1916, the German submarine U 53 made an unannounced visit to Newport, Rhode Island. After sailing, the U-Boat proceeded into international waters to intercept and sink a number of merchant ships in sight of the coast. Conducted according to the ‘stop and search’ requirements of customary international law, there was no loss of life, as passengers and crew were allowed to leave before their ships were sunk. Nevertheless, the attacks were a stark demonstration to both the Americans and the Allies of the oceanic reach of Germany’s new submarines.

That seemed at the time to have been a propaganda victory for the Germans but, in both frightening and alerting the United States, may have been a misguided initiative. The decision to attack merchant shipping without warning may have been Germany’s most significant error during the World War I, as arguably nothing but the deaths of its nationals in torpedoed ships could have brought the United States into the war.

There were other effects of the unrestricted campaigns of 1915 and 1917 that had profound consequences on Germany’s ability to wage war. The initial effort, which began in February 1915 was conceived fundamentally as a campaign of terror, in the hope that neutral merchant ships and Allied merchant seaman would be too frightened to enter the declared war zone around the British Isles. The only economic motive was the concern of German shipping interests that their share of the global carriage trade was being captured by the British, prospectively shutting them out from the revival of commerce that would follow a negotiated peace.

Despite the Allies’ deficiencies in anti-submarine warfare and shipping management, the German Navy didn’t have the numbers to make the first campaign work—there were only two U-Boats at sea in the ‘sink at sight’ area on the day it was declared. This reflected the lack of rational calculation that marked so much of the German effort. Terror was no more effective at sea than it proved to be from the air with the Zeppelin raids.

What the German Navy—and German shipowners—also missed was that global trade with Germany had been reviving rapidly by the end of 1914 and the Allied blockade proved less than effective. The British always feared that the Netherlands would be the likely conduit for illicit business with Germany and, while that country remained an important entrepôt, Scandinavia had begun to play an important role. American commercial interests were active as they sought to exploit the windfall profits that could be made. The truth was, however, that British businesses were also deeply involved. That had several causes. One was certainly the placement of profit before patriotism, occasionally to the point of outright treason, but there were other reasons. A healthy national economy, partly financed by the adversary’s hard currency, would have a better ability to sustain the expenses of war than one that didn’t have the stimulus of the additional trade. That was the reason why Napoleon created the ‘Continental System’—specifically to prevent British commerce with Europe. It took bitter internal debate before authorities such as the Board of Trade recognised that industrial war in the twentieth century required a different approach.

The U-Boat campaign had three effects, which combined to undermine the German position. First and directly, it was an ‘own goal’ in that the German submarines unknowingly sank cargoes whose final destination would otherwise have been Germany. Second, the German initiative allowed the Allies to go much further in the imposition of a blockade than international law allowed (or the Americans wanted) with the justification of reprisal. The reality that ‘the British are thieves but the Germans are murderers’ kept the US from reacting too strongly to such limitations on its commerce. Third, and perhaps most important, although it’s a point rarely made by historians, the submarine attacks and the Allied reprisals first restricted and then removed the Germans from the business world of the US. The Allies would always be better positioned to exploit the Americans’ industrial strength and their increasing ability to provide financial support, but the indirect trade with Germany that was being developed through neutral nations was on a scale—and could have become even larger—that would have ensured that significant elements in Wall Street had an interest in supporting the Germans. That would have created an obstacle to US entry to the war on the Allied side.

It’s true that the German campaign of 1917 had more economic calculations behind it than 1915, with the idea that a sustained effort by the U-Boats could sink sufficient tonnage in six months to make it impossible for an import-dependent Britain to feed itself. But those calculations were gravely flawed, as was demonstrated when the Allies were able to compensate for their staggering losses by much more effective management of their remaining tonnage, their repair and shipbuilding effort and their ports and storage ashore. The introduction of convoy was an important operational contribution, but only a part of a national and allied effort that showed how the democracies were much more effective than the ramshackle Imperial German state.

We spend much time thinking of the ‘war of territory’ that was waged on the Western and Eastern Fronts. The fact is, as U 53’s visit to Newport provided an uncomfortable reminder, the ‘war of supply’ mattered just as much between 1914 and 1918.