The 'Battle of the Mediterranean Sea' was the strategic naval campaign fought by Axis and Allied forces in the Mediterranean Sea (10 June 1940/2 May 1945).

For the most part, the campaign was fought between the Italian Regia Marina, supported by naval and air forces of Germany and Vichy France, and the British Royal Navy, supported by other Allied naval forces such as those of Australia, the Netherlands, Poland and Greece. US naval and air units joined the Allied side from 8 November 1942. The Vichy French scuttled the bulk of their fleet on 27 November 1942 to prevent the Germans seizing it. As part of the Armistice of Cassibile in September 1943, most of the Italian navy became the Italian Co-Belligerent Navy and fought alongside the Allies.

Each side had three overall objectives. The first was to attack the other side’s line of supply, the second to keep open the supply lines to their own armies in North Africa, and the third to destroy the ability of the opposing naval forces to wage war at sea. Outside the Pacific theatre, the Mediterranean saw the largest conventional naval warfare actions during World War II. In particular, Allied forces struggled to supply and retain the key naval and air base of Malta.

By the time of the Cassibile armistice, Italian ships, submarines and aircraft had sunk Allied surface warships totalling 145,800 tons, while the Germans had sunk 169,700 tons, for a total of 315,500 tons. In total the Allies lost 76 warships and 46 submarines. The Allies sank 83 Italian warships totalling 195,100 tons (161,200 by the British Empire and 33,900 by the Americans) and 83 submarines. German losses in the Mediterranean from the start of the campaign to the end were 17 warships and 68 submarines.

The Mediterranean had traditionally been a focus of British maritime power. Outnumbered by the forces of the Regia Marina, the British planned to hold the three key strategic points of Gibraltar in the west, Malta in the centre and the Suez Canal in the east. By holding these points, the Mediterranean Fleet held open vital supply routes. Malta was the linchpin of the whole system, for it provided a needed stopping point for Allied convoys and constituted a base from which to attack Axis supply routes.

The Italian dictator, Benito Mussolini, saw control of the Mediterranean as an essential prerequisite for expanding his 'New Roman Empire' into south-eastern France, the island of Corsica, Tunisia and the Balkans. Italian naval building accelerated during Mussolini’s tenure of power, in which the Mediterranean Sea came to be called 'Mare Nostrum' (our sea). Italian warships had a reputation for being well-designed, and Italian small attack craft lived up to expectations and were responsible for many successful actions in the Mediterranean. Some Italian cruiser classes were deficient in armour, however, and all Italian warships lacked radar although its lack was partly offset by their fitment with good rangefinder and fire-control systems for daylight combat. Only by the spring of 1943, barely five months before the armistice, were 12 Italian warships equipped with Italian-designed EC-3 ter Gufo radar devices. Moreover, while Allied commanders at sea had discretion to act on their own initiative, the actions of Italian commanders were closely and precisely governed by the Supermarina, the Italian naval headquarters.

The Regia Marina also lacked a proper fleet air arm. The aircraft carrier Aquila was never completed and most air support during the 'Battle of the Mediterranean Sea' was supplied by the land-based Regia Aeronautica. Another major handicap for the Italians was shortage of fuel. As early as March 1941, the overall scarcity of fuel oil had become critical, and coal, petrol and lubricants were also hard to source from local facilities. During the Italian war effort, 75% of all the fuel oil available was used by destroyers and torpedo boats carrying out escort missions.

However, the most serious problem for the Axis forces in North Africa was the limited capacity of the Libyan ports. Even under optimum conditions, this was a severe restriction of the flow of supplies. Tripoli was the largest port in Libya but could accommodate a maximum of only five large cargo vessels or four troop transports. On a monthly basis, Tripoli had an unloading capacity of 41,000 tons. Tobruk added only another 16,000 tons, and Bardia and a limited number of other but still smaller ports added a little more.

In general, the requirement of the Axis land and air forces in North Africa exceeded the capacity of the ports to deliver them. It has been calculated that the average Axis division required 9,100 tons of supplies per month. If the Italians had a fault in respect to logistics during the 'Battle of the Mediterranean Sea', it was the fact that they had failed to increase the capacity of Tripoli and the other ports before the outbreak of war.

In January 1937, France had launched a programme of modernisation and expansion. This soon elevated the French fleet to the fourth largest in the world. However, the French navy (formally the Marine Nationale) was still considerably smaller than the navy of its ally, the UK. By agreement with the British Admiralty, the strongest concentration of French warships was in the Mediterranean, for here the Regia Marina posed a threat to the vitally important French sea routes between metropolitan France and North Africa and to the British sea routes between Gibraltar and the Suez Canal.

In 1940, after the fall of France to the Germans, the Marine Nationale in the Mediterranean became the navy of the new and collaborationist Vichy France. As the Vichy French navy, this force was considered a potentially grave threat to the Royal Navy and it was seen by the British that this threat had to be neutralised. As the opening phase of the resulting 'Catapult' undertaking, Force 'X', the French squadron at Alexandria in Egypt, was rendered impotent by negotiation. This was possible primarily because the two commanders, Vice-amiral René Emile Godfroy and Admiral Sir Andrew Cunningham, were on good personal terms. In contrast, a British ultimatum to place the bulk of the remainder of the French fleet out of German reach was refused. This force, commanded by Amiral Marcel Bruno Gensoul, was based at Mers el Kébir, the port of Oran in Algeria, so on 3 July 1940 it was hit hard in 'Catapult' by the shell fire of Vice Admiral Sir James Somerville’s Force 'H' from Gibraltar. The Vichy French government broke off all ties with the British as a result of this attack and the Vichy French air force (Armée de l’Air de l’Armistice) even raided British installations at Gibraltar.

At least two Allied freighters were captured by Vichy French forces in Tunisia and later handed over to the Italian navy.

In June and July 1941, a small Vichy French naval force was involved in 'Exporter', the Allied action launched against Vichy French forces holding Lebanon and Syria. French naval vessels had to be driven off before the Litani river could be crossed.

In November 1942, as part of their occupation of Vichy France in 'Anton', the Germans intended to capture the French fleet at Toulon, but this was thwarted by determined action by French commanders, who ensured that the bulk of the fleet was scuttled at anchor.

The German U-boat campaign in the Mediterranean Sea lasted approximately from 21 September 1941 to May 1944. Germany’s Kriegsmarine aimed at isolating Gibraltar, Malta and the Suez Canal in order to break the UK’s trade and reinforcement effort to the Far East and Australasia. More than 60 U-boats were sent to disrupt shipping in the Mediterranean Sea, although many were attacked in the Strait of Gibraltar, which was controlled by the UK: nine boats were sunk while attempting the passage and 10 more were damaged. The Luftwaffe also played a major role in the 'Battle of the Mediterranean Sea', especially during the summer of 1941. In overall terms, however, the German strategy viewed the Mediterranean Sea as a secondary theatre.

It was on 10 June 1940 that Italy declared war on the UK and France, and on the following day Italian bombers attacked Malta in what was to be the first of very many raids. During this time, warships of the Marine Nationale shelled a number of targets on the north-western coast of Italy, in particular the port of Genoa. When France surrendered on 24 June, the Axis leaders allowed the new Vichy French régime to retain its naval forces.

The first clash between the rival fleets was the 'Battle of Calabria' on 9 July, just four weeks after the start of hostilities. The battle was inconclusive, and was followed by a series of small surface actions during the summer, among them the 'Battle of the Espero Convoy' and the 'Battle of Cape Spada'.

To reduce the threat to convoys sailing to Malta posed by the Italian fleet, much of which was based in the southern Italian port of Taranto, Cunningham organised the 'Judgement' operation. Fairey Swordfish single-engined biplane torpedo bombers from the fleet carrier Illustrious attacked the Italian fleet on 11 November 1940 while it was still at anchor. This was the first time that an attack of this nature had been attempted, and it was studied by Japanese naval officers in preparation for the later 'Ai' attack on Pearl Harbor. Fleet Air Arm aircraft badly damaged two Italian battleships and a third was forced to run herself aground to prevent her from sinking, putting half of the Regia Marina’s major ships out of action for several months. This attack also forced the Italian fleet to move to Italian ports farther to the north so as to be out of range of carrierborne aircraft, and this reduced the threat of Italian sallies against Malta-bound convoys.

Cunningham’s estimate that the Italians would be unwilling to risk their remaining heavy warships was quickly disproved, for a mere five days after 'Judgement', Ammiraglio di Squadra Inigo Campioni sortied with two battleships, six cruisers and 14 destroyers to disrupt a British aircraft delivery operation to Malta.

Furthermore, as early as 27 November, the Italian fleet was able to confront the Mediterranean Fleet again in the indecisive 'Battle of Spartivento'. Two of the three damaged Italian battleships had been repaired by the middle of 1941, and control of the Mediterranean continued to swing back and forth until the Italian armistice in 1943. Measured against its primary task of disrupting Axis convoys to Africa, 'Judgement' had little effect. In fact, Italian shipping to Libya increased between the months of October 1940 and 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 part of the Mediterranean Sea, the British 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'.

The 'Battle of Cape Matapan' was fought off the coast of the Peloponnesos in southern Greece on 27/29 March 1941. In this battle, Cunningham’s British and Australian warships intercepted Italian ships of the Regia Marina under the command of Ammiraglio di Armata Angelo Iachino. With the aid of radar and short-range night gunnery, the Allies sank the heavy cruisers Fiume, Zara and Pola, as well as the destroyers Vittorio Alfieri and Giosuè Carducci, and damaged the battleship Vittorio Veneto. The British lost one torpedo bomber and sustained light splinter damage to some cruisers from Vittorio Veneto's salvoes. The primary factors in the Allied victory were the effectiveness of aircraft carriers, the use of 'Ultra' intercepts and the lack of radar on the Italian ships.

The effort to prevent German troops from reaching Crete by sea as part of 'Merkur', and subsequently the partial evacuation of Allied land forces after their defeat by German paratroopers in the 'Battle of Crete' during May 1941, cost the Allied navies a number of ships. Attacks by German warplanes, mainly Junkers Ju 87 single-engined dive-bombers and Junkers Ju 88 twin-engined medium bombers, sank eight British warships: the light cruisers Gloucester and Fiji, and the destroyers Kelly, Greyhound, Kashmir, Hereward, Imperial and Juno. Seven other ships were damaged, including the battleships Warspite and Valiant, and the light cruiser Orion. Nearly 2,000 British seamen died.

This was a significant victory for the Luftwaffe as it proved that the Royal Navy could not operate in waters where the German air force had air supremacy without suffering severe losses. In the end, however, this had little strategic significance as the attention of the German army and air force were redirected toward the USSR in 'Barbarossa' just a few weeks later, and the Mediterranean was to play only a secondary role in German war planning over the following years. The action did, however, extend the Axis reach into the eastern Mediterranean, and prolonged the threat to Allied convoys.

In the 'Battle of Crete', two attempts were made to transport German troops by sea in caïques, but both of them were disrupted by British naval intervention. The tiny Italian naval escorts, however, managed to save most of the vessels. Eventually, the Italians landed a force of their own near Sitia on 28 May, when the Allied withdrawal was already taking place. During the evacuation, Cunningham was determined that the 'Navy must not let the Army down.' When army commanders stated their fears that he would lose too many ships, Cunningham said that 'It takes three years to build a ship, it takes three centuries to build a tradition.' Despite advance warning through 'Ultra' intercepts, the 'Battle of Crete' resulted in a decisive defeat for the Allies. The invasion also exacted a fearful toll on the German paratroopers, who were dropped without their major weapons, which were delivered separately in containers. So heavy were the losses that General Kurt Student, who commanded the German invasion, would later say, referring to the German decision not to use parachutists in any future invasion attempts, that 'Crete was the grave of the German paratroopers.'

After the 'Battle of Crete' in the summer of 1941, the Royal Navy regained its ascendancy in the central Mediterranean in a series of successful convoy attacks (including the 'Battle of the Duisburg Convoy' and the 'Battle of Cap Bon'), until the Italian 'Raid on Alexandria' in December temporarily swung the balance of power toward the Axis. The Regia Marina’s most successful attack on the British fleet was when divers attached limpet mines on the hulls of British battleships during the 'Raid on Alexandria' on 19 December 1941: the battleships Queen Elizabeth and Valiant were sunk at their berths, but were both raised and had been returned to active service by the middle of 1943.

Located between Sicily and North Africa, Malta was perfectly sited to interdict Axis supply convoys destined for North Africa. It could thus influence the campaign in North Africa and support Allied actions against Italy. The Axis recognised this and made great efforts to neutralise the island as a British base, either by air attacks or by starving it of its vital supplies. After a series of hard-fought convoy battles, all of them Axis victories such as the '2^nd Battle of Sirte' in March and the 'Harpoon' and 'Vigorous' convoys in June, it seemed that the island would be starved into submission by the efforts of Axis aircraft and warships based in Sicily, Sardinia, Crete and North Africa. Several Allied convoys were decimated. The turning point in the siege came in August 1942, when the British sent a very heavily defended convoy in the 'Pedestal' operation. Malta’s air defence was repeatedly reinforced by Hawker Hurricane and Supermarine Spitfire single-engined fighters flown to the island from Furious and other Allied aircraft carriers. The situation eased as Axis forces were forced away from their North African bases and eventually Malta could be resupplied and become an offensive base once again. The British re-established a substantial air garrison and offensive naval base on the island, and with the aid of 'Ultra' intelligence, Malta’s garrison was able to disrupt Axis supplies to North Africa immediately before the '2^nd Battle of El Alamein'.

The Royal Navy and the Royal Air Force sank 3,082 Axis merchantmen in the Mediterranean, amounting to over 4 million tons.

In September 1943, with the Italian collapse and the surrender of the Italian fleet, naval actions in the Mediterranean Sea became restricted to operations against U-boats and to small craft activities in the Adriatic and Aegean Seas.

On 25 July 1943, the Grand Council of Fascism ousted Mussolini, and a new Italian government, led by King Vittorio Emmanuele III and Maresciallo d’Italia Pietro Badoglio, immediately began secret negotiations with the Allies to end the fighting. On 3 September, an armistice was signed with the Allies at Fairfield Camp in Sicily, and this fact was announced on 8 September for implementation on the following day.

After the armistice, the Italian navy was split in two. In southern Italy, the Co-Belligerent Navy of the South (Marina Cobelligerante del Sud) fought for the king and Badoglio. In the north, a much smaller portion of the fleet joined the Republican National Navy (Marina Nazionale Repubblicana) of Mussolini’s new Italian Social Republic (Repubblica Sociale Italiana) and fought on for the Germans until the end of the war in Italy on 2 May 1945.