Long before the First World War, the Italian Regia Marina's First Squadron was based at Taranto, a port-city on Italy's south-east coast. In that period, the British Royal Navy developed plans for countering the power of the Regia Marina. Blunting the power of any adversary in the Mediterranean Sea was an ongoing exercise. Plans for the capture of the port at Taranto were considered as early as the Italian invasion of Abyssinia in 1935.
In 1940–41, Italian Army operations in North Africa, based in Libya, required a supply line from Italy. The British Army's North African Campaign, based in Egypt, suffered from much greater supply difficulties. Supply convoys to Egypt had to either cross the Mediterranean via Gibraltar and Malta, and then approach the coast of Sicily, or steam all the way around the Cape of Good Hope, up the whole east coast of Africa, and then through the Suez Canal, to reach Alexandria. Since the latter was a very long and slow route, this put the Italian fleet in an excellent position to interdict British supplies and reinforcements.
Following the concept of a fleet in being, the Italians usually kept their warships in harbour and were unwilling to seek battle with the Royal Navy on their own, also because any ship lost bigger than a destroyer could not be replaced. The Italian fleet at Taranto was powerful: six battleships (of which five were battleworthy, Andrea Doria having her crew still in training after her reconstruction), seven heavy cruisers, two light cruisers and eight destroyers, making the threat of a sortie against British shipping a serious problem.
During the Munich Crisis of 1938, Admiral Sir Dudley Pound, the commander of the British Mediterranean Fleet, was concerned about the survival of the aircraft carrier HMS Glorious in the face of Italian opposition in the Mediterranean. Pound ordered his staff to re-examine all plans for attacking Taranto. He was advised by Arthur LStG Lyster, the captain of Glorious, that her Fairey TSR Swordfish were capable of a night attack, using aerial torpedoes. Indeed, the Fleet Air Arm was then the only naval aviation arm capable of it. Pound took Lyster's advice and ordered training to begin. Security was kept so tight there were no written records. Just a month before the war began, Pound advised his replacement, Admiral Andrew Cunningham, to consider the possibility. This came to be known as Operation Judgment.
The fall of France and the consequent loss of the French fleet in the Mediterranean (even before Operation Catapult) made redress essential. The older carrier, HMS Eagle, on Cunningham's strength, was ideal, possessing a very experienced air group composed entirely of obsolescent Swordfish aircraft. Three Sea Gladiators were added for the operation. Firm plans were drawn up after the Italian Army halted at Sidi Barrani, which freed up the British Mediterranean Fleet.
Operation Judgment was just a small part of the overarching Operation MB8. It was originally scheduled to take place on 21 October 1940, Trafalgar Day, but a fire in an auxiliary fuel tank of one Swordfish led to a delay. (The 60 imp gal (270 L; 72 US gal) auxiliary tanks replaced the usual third crewman to extend the operating range of the aircraft enough to reach Taranto.) This minor fire spread into something more serious that destroyed two Swordfish. Eagle then suffered a breakdown in her fuel system, so she was eliminated.
When the brand-new carrier HMS Illustrious, based at Alexandria, became available in the Mediterranean, she took on board five Swordfish from Eagle, and launched the strike alone.
The complete naval task force—commanded by Rear Admiral Lyster, who had authored the plan of attack on Taranto—consisted of Illustrious, the heavy cruisers HMS Berwick and York, the light cruisers HMS Gloucester and Glasgow, and the destroyers HMS Hyperion, Ilex, Hasty and Havelock. The 24 attack Swordfish came from 813, 815, 819, and 824 Naval Air Squadrons. The small number of attacking warplanes raised concern that Judgment would only alert and enrage the Italian Navy without achieving any significant results. Illustrious also had Fairey Fulmar fighters of 806 Naval Air Squadron aboard to provide air cover for the task force, with radar and fighter control systems.
Half of the Swordfish were armed with torpedoes as the primary strike aircraft, with the other half carrying aerial bombs and flares to carry out diversions. These torpedoes were fitted with Duplex magnetic/contact exploders, which were extremely sensitive to rough seas, as the attacks on the German battleship Bismarck later showed. There were also worries the torpedoes would bottom out in the harbour after being dropped. The loss rate for the bombers was expected to be fifty percent.
Several reconnaissance flights by Martin Maryland bombers (of the RAF's No. 431 General Reconnaissance Flight) flying from Malta confirmed the location of the Italian fleet. These flights produced photos on which the intelligence officer of Illustrious spotted previously unexpected barrage balloons; the attack plan was changed accordingly. To make sure the Italian warships had not sortied, the British also sent over a Short Sunderland flying boat on the night of 11 November, just as the carrier task force was forming up off the Greek island of Cephalonia, about 170 nmi (310 km; 200 mi) from Taranto harbour. This reconnaissance flight alerted the Italian forces in southern Italy, but since they were without any radars, they could do little but wait for whatever came along. The Regia Marina could conceivably have gone to sea in search of any British naval force, but this was distinctly against the naval philosophy of the Italians between January 1940 and September 1943.
The complexity of Operation MB8, with its various forces and convoys, succeeded in deceiving the Italians into thinking only normal convoying was under way. This contributed to the success of Judgment.
The base of Taranto was defended by 101 anti-aircraft guns and 193 machine-guns, and was usually protected against low-flying aircraft by barrage balloons, of which only 27 were in place on November 11, as strong winds during preceding days had blown away the others. Capital ships were also supposed to be protected by anti-torpedo nets, but 12,800 m (42,000 ft) of netting was required for full protection, and only one-third of that was rigged before the attack. Moreover, these nets did not reach the bottom of the harbour, allowing the British torpedoes to clear them by about 60 cm (24 in).
The first wave of 12 aircraft, led by Lieutenant Commander M.W. Williamson RN of 815 Squadron, left Illustrious just before 21:00 hours on 11 November 1940, followed by a second wave of nine about 90 minutes later. Of the second wave, one aircraft turned back with a problem with its auxiliary fuel tank, and one launched 20 minutes late, after requiring emergency repairs to damage following a minor taxiing accident, so only eight made it to the target.
The first wave, which consisted of six Swordfish armed with torpedoes and six with bombs, was split into two sections when three of the bombers and one torpedo bomber strayed from the main force while flying through thin clouds. The smaller group continued to Taranto independently. The main group approached the harbour at Mar Grande at 22:58. A flare was dropped east of the harbour, then the flare dropper and another aircraft made a dive bombing attack to set fire to oil tanks. The next three aircraft, led by Lieutenant Commander K Williamson RN of 815 Squadron, attacked over San Pietro Island, and struck the battleship Conte di Cavour with a torpedo that blasted a 27 ft (8.2 m) hole in her side below her waterline. Williamson's plane was immediately shot down by the Italian battleship's anti-aircraft guns. The two remaining aircraft in this sub-flight continued, dodging barrage balloons and receiving heavy anti-aircraft fire from the Italian warships and shore batteries, to press home an unsuccessful attack on the battleship Andrea Doria. The next sub-flight of three attacked from a more northerly direction, attacking the battleship Littorio, hitting it with two torpedoes and launching one torpedo at the flagship, the battleship Vittorio Veneto, which missed. The bomber force, led by Captain O. Patch RM, attacked next. They found the targets difficult to identify, but attacked and hit two cruisers moored at Mar Piccolo hitting both with a single bomb each from 1,500 ft (460 m), followed by another aircraft which straddled four destroyers.
The second wave of nine aircraft, led by Lieutenant Commander J. W. Hale of 819 Squadron, was now approaching from a northerly direction towards the Mar Grande harbour, with two of the four bombers also carrying flares, the remaining five carrying torpedoes. Flares were dropped shortly before midnight. Two aircraft aimed their torpedoes at Littorio, one of which hit. One aircraft, despite having been hit twice by anti-aircraft fire, aimed a torpedo at Vittorio Veneto but the torpedo missed. Another aircraft hit the battleship Caio Duilio with a torpedo, blowing a large hole in her hull and flooding both of her forward magazines. The aircraft flown by Lieutenant G. W. L. A. Bayly RN was shot down by antiaircraft fire from the heavy cruiser Gorizia following the successful attack on Littorio, the only aircraft lost from the second wave. The final aircraft to arrive on the scene 15 minutes behind the others made an unsuccessful dive bombing attack on one of the Italian cruisers despite heavy anti-aircraft fire, then safely returned to Illustrious, landing at 02:39.
Of the two aircraft shot down, the two crew members of the first were taken prisoner. The other two were killed.
The Italian battleships suffered significant damage:Conte di Cavour had a 12 m × 8 m (39 ft × 26 ft) hole in the hull, and permission to ground her was withheld until it was too late, so her keel touched the bottom at a deeper depth than intended. 27 of the ship's crew were killed and over 100 more wounded. In the end, only her superstructure and main armament remained above water. She was subsequently raised and was still undergoing repairs when Italy switched sides in the war, so she never returned to service;
Caio Duilio had only a slightly smaller hole (11 m × 7 m (36 ft × 23 ft)) and was saved by running her aground;
Littorio had considerable flooding caused by three torpedo hits. Despite underwater protection (the 'Pugliese' system, standard in all Italian battleships), the damage was extensive, although actual damage to the ship's structures was relatively limited (the machinery was intact). Casualties were 32 crewmen killed and many wounded. She was holed in three places, once on the port side (7 m × 1.5 m (23 ft 0 in × 4 ft 11 in)), and twice on the starboard side (15 m × 10 m (49 ft × 33 ft) and 12 m × 9 m (39 ft × 30 ft)). She too was saved by running her aground. Despite this, in the morning, the ship's bows were totally submerged.
Italian defences fired 13,489 shells from the land batteries, while several thousand were fired from the ships. The anti-aircraft barrage was formidable, having 101 guns and 193 machine-guns. There were also 87 balloons, but strong winds caused the loss of 60 of them. Only 4.2 km (2.3 nmi; 2.6 mi) of anti-torpedo nets were actually fielded around the ships, up to 10 m (33 ft) in depth, while the need was for 12.8 km (6.9 nmi; 8.0 mi). There were also 13 aerophonic stations and 22 searchlights (the ships had two searchlights each). Denis Boyd, Commanding Officer HMS Illustrious, stated in his after-action report, "It is notable that the enemy did not use the searchlights at all during either of the attacks."
Littorio was repaired with all available resources and was fully operational again within four months, while restoration of the older battleships proceeded at a much slower pace (repairs took seven months for Caio Duilio, and the repairs for Conte di Cavour were never completed). In all, the Swordfish attack was made with just 20 aircraft. Two Italian aircraft were destroyed on the ground by the bombing, and two unexploded bombs hit the cruiser Trento and the destroyer Libeccio. Near misses damaged the destroyer Pessagno.
Meanwhile, X-Force cruisers attacked an Italian convoy. This force had three cruisers (HMS Ajax, Orion and HMAS Sydney) and two Tribal-class destroyers (HMS Nubian and Mohawk). Just past midnight, they met and destroyed four Italian merchantmen (Capo Vado, Catalani, Locatelli and Premuda), damaging the torpedo-boat Fabrizi, while the auxiliary cruiser Ramb III fled.
Cunningham and Lyster wanted to strike Taranto again the next night with Swordfish (six torpedo-bombers, seven bombers, and two flare-dispensers) – one wag in the pilot's room remarked, "They only asked the Light Brigade to do it once!" – but bad weather prevented the action.
The Italian fleet lost half of its capital ships in one night; the next day, the Regia Marina transferred its undamaged ships from Taranto to Naples to protect them from similar attacks, until the defenses at Taranto (mainly the anti-torpedo nets) were brought up to adequate levels to protect them from further attacks of the same kind (which happened between March and May 1941). Repairs to Littorio took about five months, to Caio Duilio six months; Conte di Cavour required extensive salvage work and her repairs were incomplete when Italy changed sides in 1943. Cunningham wrote after the attack: "The Taranto show has freed up our hands considerably & I hope now to shake these damned Itiys up a bit. I don't think their remaining three battleships will face us and if they do I'm quite prepared to take them on with only two." Indeed, the balance of power had swung to the British Mediterranean Fleet which now enjoyed more operational freedom: when previously forced to operate as one unit to match Italian capital ships, they could now split into two battlegroups; each built around one aircraft carrier and two battleships.
Nevertheless, Cunningham's estimate that Italians would be unwilling to risk their remaining heavy units was quickly proven wrong. Only five days after Taranto, Campioni sortied with two battleships, six cruisers and 14 destroyers to successfully disrupt a mission to deliver aircraft to Malta. The follow-up to this operation led to the Battle of Cape Spartivento on 27 November 1940. Two of the three damaged battleships were repaired by mid-1941 and control of the Mediterranean continued to swing back and forth until the Italian armistice in 1943.
The attack on Taranto was avenged a year later by the Italian navy in its Raid on Alexandria, when the Mediterranean fleet of the Royal Navy was attacked using midget submarines, severely damaging HMS Queen Elizabeth and HMS Valiant.
However, measured against its primary task of disrupting Axis convoys to Africa, the Taranto attack had very little effect. In fact, Italian shipping to Libya increased between the months of October 1940 – January 1941 to an average of 49,435 tons per month, up from the 37,204-ton average of the previous four months. Moreover, rather than change the balance of power in the central Mediterranean, British naval authorities had "failed to deliver the true knockout blow that would have changed the context within which the rest of the war in the Mediterranean was fought."
Aerial torpedo experts in all modern navies had previously thought that torpedo attacks against ships must be in water at least 75 ft (23 m) deep. Taranto harbour had a depth of only about 39 ft (12 m); but the Royal Navy had developed a new method of preventing torpedoes from diving too deep. A drum was attached beneath the nose of the aircraft, from which a roll of wire led to the nose of the torpedo. As it dropped, the tension from the wire pulled up the nose of the torpedo, producing a belly-flop rather than a nose dive.
It is likely the Imperial Japanese Navy's staff carefully studied the Taranto raid during planning for the attack on Pearl Harbor because of the issues with a shallow harbour. Japanese Lieutenant Commander Takeshi Naito, the assistant naval attaché to Berlin, flew to Taranto to investigate the attack firsthand and probably wrote a report, but no copy of such a report has ever been found. Naito subsequently had a lengthy conversation with Commander Mitsuo Fuchida about his observations in October 1941. Fuchida led the Japanese attack on 7 December 1941. More significant, perhaps, was a Japanese military mission to Italy in May 1941. Japanese Navy officers visited Taranto and had lengthy discussions with their Italian Navy opposite numbers. However, the Japanese had been working on shallow-water solutions since early 1939, with various shallow ports as the notional targets, including Manila, Singapore, Vladivostok, and Pearl Harbor. In the early 1930s, the Japanese were using a breakaway wooden nose to soften the torpedo's impact with the water. By mid-1941, the Japanese, regardless of any contribution made by studying the Taranto attack, had, through hard work and careful testing, perfected breakaway wooden fins for added aerial stability.
The Japanese attack on Pearl Harbor was a considerably larger operation than Taranto. All six Imperial Japanese fleet carriers, each one equipped with an air wing having over twice the number of planes of any British carrier, took part. It resulted in far more devastation: seven American battleships were sunk or disabled, and several other warships were destroyed or damaged. However, the Japanese raid on the United States Pacific Fleet did not alter the balance of power in the Pacific in the same way that the attack on Taranto did in the Mediterranean. In May 1942, the Japanese fleet suffered a strategic defeat in the Battle of the Coral Sea. In June 1942, it suffered a decisive defeat in the Battle of Midway: all four Japanese fleet carriers involved in the action were sunk; one of the three American carriers was also, but the other two survived essentially unscathed; the Japanese Navy never regained equality. The U.S. Navy thereafter designed its fleet operations in the Pacific Ocean around its carriers instead of its battleships as capital ships. Battleships were found to be less useful in the expanses of the Pacific than in the confines of the Mediterranean; the older ships were too slow to escort the carriers, and were chiefly used as fire support for amphibious operations.