In the early days of the Command, other arms of the RAF had priority and they had to make due with outdated planes and weapons. Supplies of aircraft were so short that many units were in fact "on loan" from the Fleet Air Arm. Their primary weapon was a small bomb that had to directly hit the submarine. This bomb had a tendency to "skip" off the water, and in one case actually hit and destroyed the plane that dropped it. Early operations were almost comical, often ending with the U-boat the victor in the rare chances they could actually be found by the aircraft.
In 1941 a experiments started to see if a depth charge could be modified to be dropped from the air. After a very successful series of tests, the bomb was quickly replaced in service with these new depth charges. In the same year a number of newer planes being introduced into the RAF Bomber Command allowed their older bomber designs to be sent to Coastal Command, including numbers of Vickers Wellingtons. These planes could operate at much longer ranges from shore, making them much more effective. The widespread introduction of sea-search radar enabled these planes to find their targets with greater ease, and soon the U-boats were being attacked throughout the Western Approaches.
About the same time the introduction of the deHaviland Mosquito freed up the Bristol Beaufighter for Coastal Command use. The Beaufighter became one of their most effective short-range aircraft, operating with rockets and depth charges against German U-boats in the Bay of Biscay. These planes were also used in attacks on other German shipping, even attacking the German flak boats originally tasked with shooting other Coastal Command aircraft down near the European shores.
Over the next two years supplies of the very long range Shorts Sunderland and B-24 Liberator allowed CC aircraft to provide the whole of the North Atlantic ocean with air cover, and losses to U-boats plummeted. It was not so much the number sunk as the constant harassment that made the planes effective, the submarines were unable to run in on the surface at night to attack, meaning that many convoys were able to sail right past the U-boats unmolested.
After WWII Coastal Command continued in its anti-submarine role. At first it continued to receive converted bomber designs, notably the Avro Shackleton, originally based on the Lancaster but soon heavily modified. With the introduction of nuclear powered designs the day of the converted bomber were over, and newer planes needed to have considerably more electronics onboard. In 1969 the special-purpose de Haviland Nimrod was introduced into RAF service for this role, and Coastal Command duties were passed onto general squadrons. The command itself ceased to exist on 28 November 1968, when it was subsumed into the new Strike Command. Today there are three active Nimrod squadrons based at RAF Kinloss, part of RAF Strike Command.