Why earlier U-boat warfare might have produced earlier convoys

If Germany had begun intensive unrestricted submarine warfare at the start of the First World War, how quickly could it have forced Britain out?

Probably not quickly: Germany initially lacked enough submarines, and the early attack could have prompted Fisher and Jellicoe to introduce convoys sooner.

The counterfactual turns on force size and institutional response. Germany lacked the large submarine fleet it assembled later in the war, while Fisher, Jellicoe, and Henderson were unusually well placed to break with established practice and introduce convoy protection. Germany would need years of construction and British inaction to force a decisive result, conditions that an early campaign would itself make less likely. A later start between Fisher's departure and Jutland offered a narrower institutional opening, but not enough time to avoid Jellicoe's return or the risk of bringing the United States into the war.