German U-boats have been attacking British shipping. Britain must trade to survive, so the Germans hoped that submarine attacks would bring the island nation to its knees. But results have been less impressive than hoped. Many British ships have been sunk but there is no sense that British trade is being strangled.
Worse, the U-boat campaign has led to increasing tension between Germany and neutral nations. To minimise risk to themselves, U-boats have been attacking ships without warning, creating a breach with maritime law as understood before the start of the war. They have also attacked ships suspected of carrying war materials to Britain, whether or not they are flying the flag of Britain or its Allies. All of this has inevitably led to loss of life among the nationals of neutral countries.
The objections of countries like Denmark or the Netherlands can be shrugged off, but tension with the United States of America is a different matter. The sinking of the Lusitania in May led to considerable loss of American life. The US government has been sending increasingly direct messages to the German government, culminating in what is effectively an ultimatum, demanding that Germany cease from endangering American lives with its U-boat campaign.
Germany cannot afford to add the United States to the list of countries it is at war with. Accordingly, the Kaiser agrees with Chancellor Bethmann-Hollweg that the U-boat campaign must be suspended. Against the objections of Admiral Tirpitz, the naval minister, a postponement of the U-boat campaign is ordered.
Our U-Boat (The Authentic History Center; the picture shows the cover of a German U-boat game for children)