The Second Happy Time (German: Zweite glückliche Zeit; officially Operation Paukenschlag ("Operation Drumbeat"), and also known among German submarine commanders as the "American Shooting Season") was a phase in the Battle of the Atlantic during which Axis submarines attacked merchant shipping and Allied naval vessels along the east coast of North America. The First Happy Time was in 1940–1941 in the North Atlantic and North Sea. Adolf Hitler and Benito Mussolini declared war on the United States on 11 December 1941, and as a result their navies could begin the Second Happy Time.

The Second Happy Time lasted from January 1942 to about August of that year and involved several German naval operations, including Operation Neuland. German submariners named it the "Happy Time" or the "Golden Time," as defense measures were weak and disorganized,^: p292 and the U-boats were able to inflict massive damage with little risk. During this period, Axis submarines sank 609 ships totaling 3.1 million tons. This led to the loss of thousands of lives, mainly those of merchant mariners, against a loss of only 22 U-boats. Although fewer than the losses during the 1917 campaign of the First World War, those of this period equaled roughly one quarter of all ships sunk by U-boats during the entire Second World War.

Historian Michael Gannon called it "America's Second Pearl Harbor" and placed the blame for the nation's failure to respond quickly to the attacks on the inaction of Admiral Ernest J. King, commander-in-chief of the United States Navy (USN). Because King also refused British offers to provide the US navy with their own ships, the belated institution of a convoy system was in large part due to a severe shortage of suitable escort vessels, without which convoys were seen as actually more vulnerable than lone ships.