Overnight, Japanese submarine I-10 launches its floatplane over the harbor at Diego Suarez, Madagascar, spotting British battleship HMS Ramillies plus a tanker, a freighter and an ammunition ship. At 5.40 PM, I-16 and I-20 send midget submarines M-16b and M-20b into the harbor from 10 miles offshore (I-18’s midget M-18b cannot launch due to engine trouble). At 8.25, M-20b fires a 17.7-inch torpedo into HMS Ramillies, opening a 30-foot hole near the forward turret (15-inch guns) and flooding magazines and shell rooms (HMS Ramillies will be towed to Durban, South Africa, for temporary repairs, then sail to Plymouth, England, in August under her own steam and return to service in June 1943). At 9.20 PM, as corvettes HMS Genista and HMS Thyme drop depth charges, M-20b fires the 2nd torpedo and sinks British tanker British Loyalty. The 2-man crew of M-20b escape but are killed by Royal Marines 3 days later.
At dawn, Japanese submarine I-25 prepares to launch her floatplane to reconnoiter Dutch Harbor Naval Operating Base and Fort Mears, on Unalaska Island in the Aleutian Islands, when lookouts spot an American cruiser. I-25 cannot dive with her plane on deck, but the cruiser passes by without noticing her.
At 6.51 AM 500 miles East of Barbados, U-155 sinks Norwegian MV Baghdad (9 dead, 21 survivors). At 10.24 AM 500 miles East of Cape Charles, Virginia, U-404 sinks US freighter SS Alcoa Shipper carrying 8340 tons of bauxite ore (7 killed 25 survivors on 3 rafts are questioned by the Germans and given several bottles of rum, cigarettes and a dungarees for a man with little clothing, then rescued 56 hours later by Norwegian steamer Margrethe Bakke).
At 9 AM, Admiral Fletcher’s Task Force 17 (aircraft carrier USS Yorktown, cruisers USS Astoria and USS Portland and 6 destroyers) leaves Pearl Harbor to meet up with Spruance’s Task Force 16. USS Yorktown has undergone minimal repairs in less than 3 days, compared to estimates of at least 2 weeks. Far from perfect, she can sail fast enough to intercept the Japanese at Midway and launch & recover her aircraft. This marvel of engineering will tip the scales at Midway and turn the tide against Japanese territorial expansion.
80 miles East of Okinawa, US submarine USS Pompano sinks the Japanese troop transport Atsuta Maru.
Despite continued Luftwaffe attacks, 21 ships from convoy PQ16 arrive at Murmansk, USSR (another 8 ships go to Archangelsk, arriving June 1).
70 miles West of Bengasi, Libya, British submarine HMS Proteus sinks the Italian merchant Bravo.
Overnight, RAF sends 1,047 aircraft (602 Wellingtons, 131 Halifaxes, 88 Stirlings, 79 Hampdens, 73 Lancasters, 46 Manchesters & 28 Whitleys) to attack Cologne, Germany, in the first 1,000 bomber raid (Operation Millennium). The goal is to overwhelm German night fighter and anti-aircraft defenses with sheer numbers. 868 bombers reach the target dropping 1,455 tons of explosives (2/3 incendiaries). 250 factories and 18,400 houses are destroyed or damaged mainly by fire (411 German civilians and 58 anti-aircraft gunners killed, 5,027 injured and 45,132 lose their homes). 41 RAF aircraft are lost.