Short answers, pulled from the story.
The wolfpack was a submarine attack strategy in which one submarine located a convoy, reported its position to a central headquarters, and other submarines converged to strike together. It was used principally by German U-boats in the Battle of the Atlantic and by the United States Navy in the Pacific.
Hermann Bauer first proposed the concept in early 1917 as commander of the High Seas U-boats. Karl Dönitz refined it into the doctrine known as Rudeltaktik, with trials in 1936 proving the revised approach successful before it was deployed in the Second World War.
The wolfpack required extensive radio communication to co-ordinate attacks, making U-boats vulnerable to the High Frequency Direction Finder, known as Huff-Duff. Allied forces could determine the location of any U-boat transmitting and move to attack it before it could strike.
The first American wolfpack departed from Midway on the 1st of October 1943. The tactics were devised by "Swede" Momsen, who led that initial mission personally.
The Happy Time was the name U-boat crews gave to the period of successful pack attacks in the latter half of 1940. It followed the shift to centralized command at Kerneval in occupied France, where Dönitz co-ordinated wolfpack operations through the Enigma code.
Wolfpacks fell out of use during the Cold War as the role of the submarine changed. With the end of convoying and the return of trade to peacetime conditions, the submarine ceased to be a commerce raider and moved to roles including scouting, intelligence-gathering, and clandestine transport.