First engagement of neutral United States in World War II before the attack on Pearl Harbor

Scholars have identified various events as being the first engagement of neutral United States in World War II before the attack on Pearl Harbor. They disagree on which events led to formal entry of the United States into the conflict.
Attacks by the U.S. military.
The first American hostile action against Axis forces was on 10 April 1941, when the destroyer attacked a German U-boat: the "U-52", which had just sunk the Dutch freighter "Saleier" near Iceland. "Niblack" was picking up survivors of the freighter when it detected "U-52" preparing to attack. The "Niblack" attacked with depth charges and drove off the U-boat. There were no casualties on board "Niblack" or the U-boat. By coincidence, USS "Niblack" was later in the same convoy as, and picked up survivors from, the USS "Reuben James" when that ship was sunk.
The first American hostile action against Axis forces that resulted in physical destruction was on 14 September 1941, when destroyed a German weather station in northeast Greenland. The action was based on an agreement with Danish Ambassador to the United States Henrik Kauffmann in April 1941 to patrol the Danish island.
The first American-caused casualties occurred on 7 December 1941 when the attacked and sank a Japanese midget submarine near the entrance to Pearl Harbor prior to the commencement of the Japanese air attack upon Hawaii later that day. As a result of the attack on Hawaii, America declared war on Japan on 8 December 1941. Germany and Italy declared war on the United States three days later.
The first planned offensive action by the United States in World War II came in January 1942 when the aircraft carrier attacked Japanese bases in the Marshall Islands.