America's Undeclared Naval War in the Atlantic, 1939–1941

Introduction

America's decision to escort convoys into the Atlantic signaled its readiness to enter an undeclared naval war with Germany during World War II, and yet these very actions have been the subject of considerable criticism. Many claimed the Roosevelt administration failed to establish clear defensive strategies that would have adequately protected the United States. Some argue the country was effectively a sitting duck until the moment it was attacked. Others contend that U.S. security decisions were deeply shaped by broader international circumstances — most notably, that if Britain were to collapse under the weight of war, the Axis powers would essentially control the resources of the entire Old World, leaving the New World surrounded by conflict.

This paper examines the United States' undeclared war in the Atlantic, analyzing it both as a defensive measure against the potential spread of European war and as what some historians regard as a deliberate strategic maneuver to draw the U.S. into direct conflict with the Axis powers. It also considers Germany's U-boat strategy as a central element of that confrontation.

Overview of U.S. Neutrality and Early War Involvement

In September 1939, President Roosevelt sought to support the Allies while constrained by the Neutrality Acts from formally entering the war in the Atlantic (Kershaw, 2007). Roosevelt initiated efforts against the Nazis only after learning that Britain intended to defy Germany. Following this, he made plans to ship war material and began preparing what became the Lend-Lease arrangement (Kershaw, 2007; Bailey & Ryan, 1979), which assisted in financing the British war effort.

By April 1941, what had previously been a 300-mile Western Hemisphere Security Zone was extended to include Greenland and the Azores (Kershaw, 2007). The U.S. Navy thereby became authorized to escort British convoys, essentially entering undeclared war with Germany in the North Atlantic (Bailey & Ryan, 1979; Kershaw, 2007). Because the Red Sea was no longer listed among forbidden combat zones, Lend-Lease supplies could now reach the British through that route via North Africa.

By the end of 1940, America's defense program was well established and supplies were flowing to Great Britain. However, the British were no longer able to pay cash for the war materials they needed. President Franklin Roosevelt therefore presented a plan to Congress, proposing the Lend-Lease bill that would provide large-scale aid to Britain and the other Allies. In 1941 this bill passed and became law, with Congress appropriating seven billion dollars for materials to be sent to the Allies (Patterson et al., 2009). The act was widely regarded as an unofficial declaration of war against the Axis powers and strengthened the unwritten alliance between Britain and the United States. Simultaneously, Nazi submarines intensified their attacks on British ships in the North Atlantic in an effort to cut off American supplies. Roosevelt responded by ordering naval vessels to support the British through submarine patrols in the Atlantic.

A series of significant incidents followed. On April 11, the U.S. destroyer Niblack fired depth charges on a German U-boat — considered the first hostile action by a U.S. Navy vessel in the undeclared naval war (Kershaw, 2007). The U.S. Navy subsequently began observation patrols within the Security Zone. On May 21, a German U-boat sank the U.S. freighter Robin Moor (Bailey & Ryan, 1979; Kershaw, 2007). Hitler then ordered Admiral Dönitz's U-boats to avoid American warships, and those orders were followed. Nevertheless, because British and Canadian vessels frequently operated alongside U.S. warships, German U-boats were effectively forced to absorb attacks without the ability to counterattack — a historically significant constraint on their operations (Kershaw, 2007).

Naval Incidents and the Escalation of Undeclared War

The United States was still not formally at war. It was not until Iceland invited U.S. intervention that American forces moved in July to replace British troops, pushing U.S. naval presence further into waters where the Royal Navy had been battling U-boats (Kershaw, 2007; Bailey & Ryan, 1979). War at that point seemed inevitable. Churchill and Roosevelt met privately to discuss formal U.S. entry, though the United States maintained its public commitment to democracy and neutrality. There was no widespread public outrage over the ongoing incidents, even after U-boats sank another U.S. freighter in September 1941 (Kershaw, 2007). Incidents and losses continued to mount. Later that year, the freighter Greer was sunk in what was described as an act of piracy. In November, the Senate revised the Neutrality Act to allow merchant vessels to arm themselves and to permit U.S. ships to enter combat zones. The American public largely supported the President in all measures that stopped short of formal war.

By June 1941, the U.S. Navy was actively protecting ships carrying Lend-Lease materials to Britain, and with that commitment the United States was, in practical terms, involved in an undeclared war against Germany (Patterson et al., 2009).