As soon as the U.S. declared war, Germany sent u-boats to harass shipping along the U.S. east coast. The first German u-boats began operating there in January 1942. East coast shipping included not only ships that routinely plied the coastal trade, but also those bound to and from trans-Atlantic convoy runs. The convoys usually assembled in Halifax and ships bringing goods form all up and down the coast sailed north to join them. No north-south convoys were established yet, so ships sailed independently and unescorted. The German boats rested on the bottom by day and hunted at night. Ships were torpedoed within sight of people on the shore. Amazingly, as gunfire could be clearly heard by tourist on the beaches, as fires from stricken ships lit the night sky, and as oil and bodies washed ashore from sunken ships, cities along the coast refused to participate in a nighttime blackout. It was claimed that darkness would hurt the tourist industry. So ships sailed offshore, clearly silhouetted by the lights on shore. The German captains called this the “Happy Time”.
The Coast Guard was charged with protecting the coastal shipping lanes. The main weapons against the u-boats were the “B” class 165-foot Argo/Thetis-class and 125-foot Active-class cutters, plus a variety of tenders, tugs, and converted yachts. All together, there were about 70 ships for the entire coast. Aircraft aided in the search missions. The Navy complimented the patrols with older destroyers.
The early months did not go well. Cutters spent most of their time rescuing sailors from sunken ships, salvaging stricken ships that did not sink, and marking sunken ships as hazards to navigation. Finally, in March, Navy aircraft sank two u-boats, and in April, USS Roper nailed another. On 9 May, USCGC Icarus nailed U-352. LT Maurice Jester was awarded the Navy Cross. May also saw the inauguration of north-south escorted convoys and mandatory blackout conditions for all coastal cities. On 13 June USCGC Thetis, commanded by LTJG N.C. McCormick, nailed U-157. On 1 August, a Coast Guard J4F piloted by Chief Aviation Pilot Henry White and crewed by RM1 George Boggs sank U-166 with a single well-placed depth charge. This was the only Coast Guard air victory over a u-boat in the war. White was awarded a DFC and Boggs an Air Medal. In the first six months of the war, the U.S. had sunk only six u-boats and the Coast Guard accounted for three of them. Germany had built 123 more. U-boats had claimed 400 ships. Among the casualties was USCGC Acacia, a buoy tender sunk by deck guns by U-161. But the new convoy system and the blackout worked. This, coupled with newer, more capable escort vessels coming into the fleet, began to turn the tide. At the end of August, Germany pulled her u-boats form the coast in search of easier prey. Individual boats still forayed to the coast, but Happy Time was over.
In the Caribbean Sea, the Coast Guard manned eight corvettes, 208-foot vessels built in Canada and commissioned between November 1942 and August 1943. All were principally employed escorting coastal convoys between Florida and Guantanamo Bay, Cuba. It was rather monotonous duty enlivened by an occasional sonar contact and more frequently by rough weather, in which the little ships justified their reputation for seaworthiness, and for lack of sea kindliness. They also acquired four SC-1-class sub chasers of WWI vintage.
For a complete list of cutters engaged in coastal convoys go to this Link.