With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: The United States declared war upon Germany in April 1917 after fears of German submarines in their careful and controlled targeting of British military shipping was nonetheless harming American trade relations. With the U.S. mobilizing for war, President Woodrow Wilson appointed Hoover to head the U.S. Food Administration, which was charged with ensuring the nation's food needs during the war. Hoover had hoped to join the administration in some capacity since at least 1916, and he obtained the position after lobbying several members of Congress and Wilson's confidant, Edward M. House. Earning the appellation of "food czar", Hoover recruited a volunteer force of hundreds of thousands of women and deployed propaganda in movie theaters, schools, and churches. He carefully selected men to assist in the agency leadership—Alonzo Taylor (technical abilities), Robert Taft (political associations), Gifford Pinchot (agricultural influence), and Julius Barnes (business acumen).
text_B: Given what can be learned from this passage, would it be reasonable to assume that uniformed American sailors had been fired up, and possibly even killed, by German U-Boats prior to April of 1917 without this technically being an act of war against the US?
NO.