Why U-boats could not isolate Britain

Could a larger German U-boat effort have starved Britain or kept the United States out of the war?

It could have imposed heavier costs, but it was unlikely to force British surrender or overcome eventual American shipbuilding capacity.

In this assessment, Britain was unlikely to surrender simply because Germany expanded E-boat or U-boat operations. Even before considering American intervention, British access to nearby food supplies complicated a simple starvation scenario. Once the United States committed itself, American industrial capacity could build shipping faster than Germany could destroy it. French shipyard capacity might have helped, but submarine construction was technically vulnerable to disruption and could not erase the wider Allied material advantage.