The campaign began against an unfavourable land-war balance, with 190 Allied divisions in Europe against 150 German divisions in January 1917. Germany opened the maritime offensive with 105 submarines ready and maintained roughly 120 available through much of the year despite losses and new-crew demands. Sinkings approached the target in February and March, reached about 860,000 tons in April, and left Britain described as having only six weeks of food supply. Germany lost just nine submarines in the campaign's first three months, so the early operational figures looked close to Holtzendorff's forecast. The political result was immediate: President Wilson severed diplomatic relations on 3 February, and Congress declared war on 6 April. That short-term operational success came with the strategic cost of another great power entering the conflict.
Chapter · 36:05-37:48
Early U-boat success and American entry
Early 1917 sinkings brought Britain close to a supply crisis, but they also triggered the American break with Germany and declaration of war.