The German submarine U-56, commanded by Lieutenant Wilhelm Zahn, found itself bang in the middle of a contingent of the British Home Fleet sailing just west of the Orkney Islands. Leading the contingent was the battleship HMS Rodney followed by the HMS Nelson and HMS Hood, all surrounded by a protective screen of destroyers. Here was the U-56, sitting at periscope depth in an ideal firing position and straight ahead was the Flagship of the Fleet, HMS Nelson. Elated, Zahn fired three torpedoes at the target which was impossible to miss. Two of the torpedoes actually hit the Nelson but did not explode! The U-56 made a quick getaway. Had the torpedoes exploded, the V.I.P.s on board the Nelson would have been in great danger. They had gathered for a conference to determine what action had to be taken after the sinking of the Royal Oak at Scapa flow. The illustrious guests included the C-in-C Home Fleet, Admiral Sir Charles Forbes, the First Sea Lord, Admiral of the Fleet, Sir Dudley Pound, and Lord of the Admiralty, Mr.Winston Churchill! This heaven sent opportunity caused Admiral Karl Donetz, the German U-boat supremo, to write in his war diary "Without doubt, the torpedo inspectors have fallen down on their job ... at least 30% of our torpedoes are duds!" Gunther Prien, hero of Scapa Flow, remarked "How the hell do they expect us to fight with dummy rifles". Without doubt this was a great embarrassment to the German Navy - 31 U-boat attacks from favourable positions, 4 attacks on the Warspite, 12 attacks on various cruisers, 10 attacks on destroyers and 5 attacks on troop transports - without a single hit! All torpedoes failed to explode. How lucky we were!
I think one of the biggest disasters of World War II, in regards to maritime warfare, was the sinking of the U.S.S. Indianapolis:
The USS Indianapolis (CA-35) was commissioned at the Philadelphia Navy Yard on 15 November 1932. The ship served with honor from Pearl Harbor through the last campaign of World War II, sinking in action two weeks before the end of the war. At 12:14 a.m. on July 30, 1945, while sailing from Guam to Leyte, Indianapolis was torpedoed by Japanese submarine I-58. The ship capsized and sank in twelve minutes. . The remainders, about 900 men, were left floating in shark-infested waters with no lifeboats and most with no food or water.
Survivors were spotted by a patrol aircraft on 2 August. All air and surface units capable of rescue operations were dispatched to the scene at once, and the surrounding waters were thoroughly searched for survivors. Upon completion of the day and night search on 8 August, 316 men were rescued out of the crew of 1,199.
The ship's captain, the late Charles Butler McVay III, survived and was court-martialed and convicted of "hazarding his ship by failing to zigzag". Despite overwhelming evidence that the Navy itself had placed the ship in harm's way, despite testimony from the Japanese submarine commander that zigzagging would have made no difference, and the that fact that, although over 350 navy ships were lost in combat in WWII, McVay was the only captain to be court-martialed. Materials declassified years later adds to the evidence that McVay was a scapegoat for the mistakes of others.
They were on a secret mission to deliver the first atomic bomb to Tinian Island. On their return leg home, they were torpedoed and left for the sharks, because no one knew what happened.
Well hands down the worst maritime disaster of WW2 was the Halifax Harbour Explosion. Munitions ship ran into another ship in themiddle of the harbour and a fire started and then thousands of tons of TNT, and other volatile explosives levelled the nearby buildings, vapourized human beings, deposited pieces of ship's hull miles inland and it all happened off the tranquil coast of Canada's largest maritime province harbour. Can't beat that.