Admiralty scientists led by Dr. C F Goodeve and Dr. E C Bullard have found a way to defeat the magnetic mine threat. Since the mines are detonated by a ship's magnetic field, a system of cancelling this out has been developed. Ships will be fitted with electric cables passed round the hulls and connected to the generators. Known as "degaussing," this will create a magnetic field exactly opposite to the ships.

Methods have also been found for sweeping for these mines. Experiments using wooden trawlers towing sweeps made up of energised electrical cables have proved successful in detonating them. A Vickers Wellington IA (P2518), was taken off the production line at Weybridge and fitted with a large magnetic coil 48 feet in diameter attached to the underside of the nose, tail and outer planes. Fed with electrical power from a 35kW Maudesley generator driven by a Ford V8 engine the aircraft still had to fly as low as 60 feet above the water to ensure detonation.

Destroyer HMS Havant commissioned.

GERMANY: The surface raider 'Atlantis' (7,862 ton, ship number 16) is re-launched, after conversion from the freighter 'Goldenfels'. She will be referred to by the British as Raider C. (Alex Gordon)

U-70 laid down.

FINLAND: After the Soviet attack to Finland, Soviet battleship Marat tried to destroy Fort Saarenpää. However, the defenders claimed at least one artillery hit on Marat and the ship was forced to retreat with damages.

CANADA: Liner SS Prince David purchased from Canadian National Steamship Lines for conversion to AMC HMCS Prince David, commissioning 28 Dec 1940. Armed merchant cruisers were used to supplement the escort of convoys against large enemy surface warships. The RN was unable to provide either battleships or cruisers to act as escort for all convoys and resorted to using converted liners instead. AMCs suffered heavy losses to submarines because of their size made them obvious targets. The AMCs were eventually removed from service and converted to troop transports as the threat from German surface raiders was reduced. In the early spring of 1941, while steaming alone in the North Atlantic, Prince David sighted the masts and upper superstructure of a large enemy warship. Believing the ship to be a battleship and knowing no allied vessels were in vicinity, Prince David reversed course and increased to her full speed of 22 knots. The German also turned away, assuming that his adversary was a cruiser. Neutral US patrol planes later reported the German warship as a Deutschland-class armored ship or ‘pocket battleship’. The enemy ship was likely Admiral Scheer, which was returning home in Mar 41 from its successful cruise in the South Atlantic and Indian Oceans. Prince David’s WWI-vintage 6-inch and 3-inch guns, all of which were locally controlled, would have been no match for the German 11-inch and 5.9-inch guns, which were controlled by a modern direction and fire control system.

ATLANTIC OCEAN: British destroyer HMS Hyperion intercepts the German passenger liner SS Columbus 450 miles (724 kilometres) east of Cape May, New Jersey; the latter is scuttled to prevent capture. Two crewmen perish in the abandonment. The USN heavy cruiser USS Tuscaloosa (CA-37) rescues Columbus's  survivors (567 men and 9 women stewardesses) and sets course for New York City, the only U.S. port that can handle such a large and sudden influx of aliens.

     Meanwhile the British light cruiser HMS Orion intercepts the German freighter SS Arauca off Miami, Florida; the latter puts in to Port Everglades to avoid capture. Destroyer USS Truxtun (DD-229) has trailed the merchantman at one point; destroyer USS Philip (DD-76) is present when Arauca reaches sanctuary. A USAAC B-18 Bolo of the 21st Reconnaissance Squadron (Long Range) based at Miami Municipal Airport, however, witnesses the shot that HMS Orion fires over Arauca's bow (in the attempt to force the latter to heave-to) splashing inside U.S. territorial waters off Hialeah, Florida. Learning of this incident, Secretary of State Cordell Hull instructs U.S. Ambassador to the Court of St. James Joseph P. Kennedy to remind the British Foreign Office that, as neutrals, the American republics are entitled to have their waters "free from the commission of any hostile act by any non-American belligerent nation." SS Arauca is interned by the U.S. government and is acquired by the U.S. Navy from the Maritime Commission on 20 April 1942 and commissioned as the refrigerated storeship USS Saturn (AF-40)  the same day.

U-60 sank SS City of Kobe.