What role did the Coast Guard play in World War II?
Alright, Anon, the TL;DR answer to this question is a whole heck of a lot.
In 1940, as the United States geared up for war with Germany, President Franklin Roosevelt issued an executive order than placed the Coast Guard under the jurisdiction of the U.S. Navy. One of the first things the CG did was execute what is known as the Greenland Patrol. Greenland possessed resources valuable to the war and FDR used Germany’s invasion of Denmark to justify having a CG station there. This station was maintained throughout the war.
Coast Guard Cutters played a role in the Battle of the Atlantic, both in terms of chasing and sinking U-boats, escorting convoys across the Atlantic, and performing rescue operations for ships sunk by U-boats. Convoy duty and sub hunting were common assignments in the Pacific theater as well.
The Coast Guard also manned landing craft for Allied forces. They were present during the invasion of Normandy as well as dozens of D-days in the Pacific. They manned landing craft during these operations as well as support craft.
At home the Coast Guard continued beach patrols, port security, and the like. The Coast Guard contributed a significant amount of men and material to the war effort but they are largely forgotten about. For more reading you can check out the Coast Guard’s history site here or pick up The United States Coast Guard in World War II by Thomas Ostrom.