How close unrestricted submarine warfare brought Britain to starvation

How close did German submarines bring Britain to starvation in the First World War?

Contemporary estimates gave Britain about ninety days of food, while the practical margin may have been roughly one hundred to 110 days.

Jellicoe and an American admiral estimated that Britain had about ninety days of food remaining. The country might have stretched that margin to roughly one hundred or 110 days, only about two additional weeks. The danger peaked after shipping losses exceeded 800,000 tons in a single month during 1917. Britain did not approach the same margin in the Second World War, making the First World War episode the sharper example of merchant-shipping attrition becoming a national survival issue.