There are several reasons for the oversight of the exact maritime casus belli among historians. By contrast to the more famous earlier attacks on British passenger ships, such as the Lusitania and the Arabic, the U.S. merchant ships were manned by low-status, underpaid, merchant mariners, who were of far less concern to Wilson than were the middle- and upper-class passengers on foreign-flag passenger liners.

Germans attack four American merchant ships

The United States Merchant Marine provided the greatest sealift in history between the production army at home and the fighting forces scattered around the globe in World War II. The prewar total of 55,000 experienced mariners was increased to over 215,000 through U.S. Maritime Service training programs.