At the outbreak of World War Two the Royal Navy had 180 destroyers, with 140 lost to enemy action during six years of conflict. To offset this attrition, 220 destroyers were built and 50 acquired from the USA via the bases-for-ships deal. The most crucial challenge for the RN’s destroyer force in WW2 was the Battle of the Atlantic, which peaked in May 1943. As in WW1, the German U-boats nearly won the battle. Their aim, again, was the destruction of so many merchant ships that Britain would be starved out of the war through lack of supplies. In the early part of the conflict, the Germans adopted an aggressive policy of combining surface raiders with submarines, but the former proved ineffective. On the British side in the early days, hunting groups capable of destroying enemy submarines, and hindering surface raiders, were formed around aircraft carriers. This tactic proved to be disastrous, with the needless loss of the carrier Courageous - a converted WW1 battle-cruiser - in September 1939, proving emphatically that looking for trouble could only end in disaster. It was better to ride with the U-boats’ prey and let them come to you, rather than go on wild goose chases. IN the summer of 1940 many RN destroyers had to stay close to home in case they were needed to destroy a German invasion fleet. Destroyer escorts were therefore scarce on the Atlantic convoy routes. In general, the most modern destroyers were used for fleet and coastal protection duties while the older ones were ordered to ride shotgun on the convoys, as well as carry out shore bombardment missions and mine-sweeping. Smaller, slower, Hunt Class escort destroyers, which were entering service at the outbreak of war, were more suited to escort work than faster vessels, but they were not readily available. So, until the newer, more capable escort vessels could be released from home duties, the RN used elderly WW1-era ‘Lend-Lease’ destroyers which the Americans had handed over in return for the use of British military bases overseas. Construction of Anti-Submarine Warfare sloops and corvettes also got underway, but it would be some time before any of them were ready. The older, home-built, V and W destroyers were also converted to the long-range escort role. In the meantime, the RAF played a crucial supporting role in combating the U-boat menace, until June 1940, by flying long-range patrols. However the start of the RAF’s bomber offensive against Germany meant that many of the long range planes were withdrawn for that campaign. Between June and December 1940 U-boats sent three million tons of shipping to the bottom and only 16 actively patrolling U-boats inflicted this damage. It was very worrying for the Admiralty that, even with these small numbers, the Germans were gaining the upper hand. The situation worsened at the beginning of 1941, as by then German shipyards were able to produce 20 new U-boats a month for the Kriegsmarine. The Luftwaffe was also doing its bit, running long-range patrols with Condor aircraft and launching strikes by shorter range bombers whenever possible. The U-boats, the Luftwaffe and surface raiders managed to destroy 800,000 tons of British merchant shipping in the first half of 1941. But, the British were lucky that the Germans provided them with a crucial breathing space by failing to press home their Luftwaffe advantage. German air force chiefs put little priority on Condor patrols and strikes by land-based bombers against British shipping. Soon, however, aircraft were being diverted to allegedly more worthwhile tasks, such as flying against the Russians on the Eastern Front. In April 1941 RAF Coastal Command came under Admiralty control and the conversion of destroyers into long-range escorts was well underway. Also, with Hitler’s invasion of Russia, it was plain he had abandoned plans for launching an assault across the English Channel and so the destroyers that had been sticking close to home were now released for convoy escort work. But still, despite increasing US and Canadian involvement in the Battle of the Atlantic, losses were very high. Close to 1,000 Allied merchant ships were sunk in 1941 as U-boat strength had quadrupled. However, the capture of a German Enigma coding machine aboard U-110, in early May 1941, was a turning point. This enabled British code-breakers to fully penetrate signals between patrolling German U-boats and German Navy HQ. At the same time the system of integrated escort groups made its debut. The real turning point of the Battle of the Atlantic came between February and May 1943. By that time the Germans had 240 U-boats in service, 50 of them at sea at any one time. In February 1943, 48 Allied merchant ships were sunk for the loss of 22 U-boats. In March, 105 merchant ships were lost for the destruction of 16 U-boats. But by April there were only 25 merchant ships lost for the destruction of 16 U-boats - clearly an unacceptable margin for the Kriegsmarine. In May, 46 U-boats were sunk and the Germans were forced to throw in the towel, withdrawing from the Atlantic. Following this admission of defeat their U-boat arm, understandably, lost its vigour, although patrols continued until the end of the war. For both sides the Battle of the Atlantic was a bloody and bitter affair. The German submarine losses were simply staggering. Of 1,162 German submarines in service during WW2 - 785 were sunk. Other statistics of the appalling losses incurred include 2,400 merchant ships sunk and Royal Navy and dominion naval losses of 47 destroyers and other escorts, one battle-cruiser (Hood), two cruisers and three aircraft carriers.
This is a good source of information on the 50 "Land-Lease" destroyers provided by the US: http://www.navweaps.com/index_tech/tech-072.htm
