By the end of June in 1940, the German war machine had claimed Poland, Denmark, Norway, Netherlands, Belgium and France leaving Britain to fend for itself with nothing but Channel water between it and German-held territories. From the German point of view, if enough damage could be inflicted upon Britain's commercial sea traffic arriving from America and far-off parts of the Empire, she could be starved into surrender. A policy of unrestricted submarine warfare was implemented by the Kriegsmarine (German Navy) from the beginning of World War 2. As such, U-Boat submarines threatened the central Atlantic, an area so vast and far from land that conventional aircraft were unavailable to supply cover over the convoy routes. Add to this the fact that the Allies had not, to this point, implemented a policy of armed escorts for its convoys. Instead, the strategy was to use anti-submarine resources to simply hunt down enemy U-boats and set up patrol boat "traps" in areas that German submarines had to pass through to enter the kill zone that was the Atlantic Ocean. However, this strategy ultimately proved a failure and it became apparent that all Allied convoys would require armed escorts as they crossed the Atlantic.
The corvettes of the Flower-class were built to save the Atlantic Convoys. The government's low-cost proposal was accepted by Smith's Dock Works of the United Kingdom in 1939. They used the latest design of their Arctic whaler as a starting point and then increased the overall length of these vessels by 30 feet to 205 feet. They were small warships, having minimal armament, depth charges and the latest sonar while conditions for the crew were cramped and uncomfortable. The vessels were needed in large numbers and some 288 were built to help cover the escort requirement. The Allies did not have enough trained seamen so the crews were comprised mostly of reservist naval personal. Flower-class ships were small enough to be built in civilian boat yards across Canada, France and the United States. Even the Kriegsmarine used a number of the class when captured in French ports as they were under construction and could not steam away in time.
HMCS Sackville was a Flower-class corvette built at the Saint John Shipbuilding and Dry Dock Company of Saint John, New Brunswick in early 1940. She was listed as "Patrol Vessel 2", the second ship built in Saint John. 288 Flower-class corvette ships were built during World War 2. She served in the Royal Canadian Navy protecting convoys between Canada and the United Kingdom. After America was attacked in December of 1941, convoys were also protected to and from the east coast of the United States.
Sackville drew only 11.5 feet of water so her design was perfect to patrol for submarines operating close to the English and Canadian coasts. Her range was also good at 3,500 nautical miles (6,482 km) when heading at 12 knots (22.2 km/h) so she could screen tankers and cargo vessels from the United Kingdom to Canada with fuel to spare. Sackville was finished with a single 4-cycle, triple-expansion, reciprocating steam engines that proved efficient in producing more steam using less coal which was needed to reduce the weight of coal carried onboard over long cruises.
Crews had trouble living and working on the Flower-class due to her small size as she rolled and bobbed up and down in heavy seas making many of the crew sea sick. As small as they were, the Flower-class were able to negotiate the rivers leading to the Great Lakes where some were built. They were fitted with magnetic compasses which were reliable during heavy weather or during depth charging of German submarines. The first ships were equipped with older obsolete sonar having a fixed transducer. This arrangement was second rate as the sonar contact with the submarine would be lost due to vibration when the depth charges were detonated under water.
To locate enemy submarines, HMCS Sackville was later equipped with the upgraded Type 144c sonar and Type 271 SW2C surface radar. When a contact was made on the surface, the ship would attack with the 4-inch BL (101.6 mm) Mk.IX single deck gun located at the bow. Normally the contact was made when the submarine was below the surface. Sackville would make runs over the sonar contact looking for the location and depth of the submarine. When the sonar registered a large metal object they would start dropping the depth charges from two depth charge rails located on the stern. The ship carried a total of 40 depth charges as built which was increased to 70 in time. An Mk 3 Hedgehog anti-ship mortar launching system was placed on board and able to launch six smaller depth charges in a dispersal pattern to help counter the loss of the submarine contact. The Hedgehog mortar was added allowing the ship to stand off while firing the mortar depth charges allowing the sonar to maintain contact with the sub. To repel aircraft, the ship had 1 x 2-pounder single-barreled anti-aircraft mount, 1 x QF Mk.VIII gun, 1 x twin-barreled 20mm Oerlikon gun and 2 x Lewis .303 caliber machine guns - one fitted to port and other to starboard.
During the war years the class had many upgrades made, some based on the theater of war to which they were assigned to. In the beginning, all the class had been equipped with minesweeping gear however most of the class that did escort work in the Atlantic had the gear removed to improve range. Many had the galley relocated from the stern to midships to allow for extra depth-charge storage racks. When the need to increase the number of depth charges for the Atlantic runs arose, they were stowed along walkways. The forecastle was lengthened to midships to provide increased crew accommodations and give the ship better sea keeping stability in heavy seas. Sea keeping stability was also increased with the bow becoming more pronounced. The bridge was lowered and elongated with the removal of the as-built compass house. Anti-aircraft protection was needed so additional twin Lewis guns were mounted on the roof of the bridge. Normally 2 x Oerlikon 20mm cannons were placed on the bridge wings, however, in areas where enemy aircraft were a major threat, up to six cannons were used.
HMCS Sackville was used on the Atlantic run and Canadian shore patrol. From February 1942 to July 1944 she provided protection for 30 convoys containing 1,380 merchant ships manned by 90,000 seamen only loosing 9 ships sunk by enemy U-boats. She did not sink any U-boats herself but battled four submarines by keeping them occupied and away from the merchant ships or by damaging them, forcing the U-boats to disengage from the battle. During World War 2, 36 Flower-class corvettes were sunk by Axis submarines or aircraft and some by collision with Allied ships. The class sank or participated in the sinking of 47 German and 4 Italian submarines, mostly in the Atlantic.
In 1945 after the war, most Flower-class corvettes were scrapped or sold to friendly governments. Sackville was laid up in reserve for seven years then reactivated in 1952 when a Canadian agency, the Department of Marine and Fisheries, required a ship. Sackville was chosen because of her size and her shallow draught which would allow her access to shallow Canadian waters. Her armament was removed and she was converted as a research vessel. She was given a new pennant number, 532, painted on the hull then changed to 113 in 1958. A laboratory was built on the aft superstructure in 1964 so marine life and water samples could be inspected at the source. Now pennant number 113 remained in service in the rivers and coastal waters on the east coast of Canada until July of 1982 when she was retired from the Department of Marine and Fisheries.
In October of 1983, the decision was made to keep her a protected museum ship. HMCS Sackville was reassigned to the Canadian Naval Corvette Trust to be restored to her 1944 appearance including the original dazzle camouflage while reusing hull number K181. Her armament was found and refitted along with crew quarters and dummy ammunition. Today, she serves as a museum ship moored beside the Maritime Museum of the Atlantic in Halifax, Nova Scotia, and can be toured during the summer months.