The 'Raid on Bari' was an air attack by German bombers on Allied forces and shipping in Bari, Italy (2 December 1943).

A force of 105 Junkers Ju 88 twin-engined medium bombers of Generalfeldmarschall Wolfram Freiherr von Richthofen’s Luftflotte II achieved total surprise and bombed shipping and personnel operating in support of the Allies' campaign in Italy, sinking 27 cargo and transport ships, as well as one schooner, in the harbour of Bari on the south-western coast of the Adriatic Sea. The attack lasted a little more than an hour and put the port out of action until February 1944. The release of mustard gas from one of the wrecked cargo ships added to the loss of life. The British and US governments concealed the presence of mustard gas and its effects on victims of the raid.

Early in September 1943, coinciding with the Allied 'Avalanche' invasion of Italy at Salerno, Italy surrendered to the Allies in the Armistice of Cassibile and changed sides, but the new Italian Social Republic in central and northern Italy continued the war on the Axis side. On 11 September 1943, the port of Bari in southern Italy was taken unopposed by Major General F. A. M. Browning’s British 1^st Airborne Division. The port was used by the Allies to land ammunition, supplies and provisions from ships at the port for Allied forces advancing towards Rome and to push German forces out of the Italian peninsula.

Bari’s air defences were wholly inadequate air defences: no Royal Air Force fighter squadrons were based there, and such fighters as were within range of the port were assigned to escort or offensive duties rather than port defence. The ground defences were equally ineffective.

Little thought was given to the possibility of a German air raid on Bari, because it was believed that the Luftwaffe in Italy was stretched too thinly to mount a serious attack. On the afternoon of 2 December 1943, Air Marshal Sir Arthur Coningham, commander of the North-West African Tactical Air Force, held a press conference in which he stated that the Germans had lost the air war, and added that 'I would consider it as a personal insult if the [Germans] should send so much as one plane over the city.' This statement was made despite the fact that German air raids by Oberstleutnant Volprecht Riedesel Freiherr zu Eisenbach’s Kampfgeschwader 54 'Totenkopf', Oberstleutnant Rudolf Hallensleben’s KG 76 and other units had hit the port area of Naples four times in the previous month, and attacked other Mediterranean coastal targets.

There were 30 ships of US, British, Polish, Norwegian and Dutch registry in Bari harbour on 2 December, and the adjoining port city had a civilian population of 250,000 persons. The port was lit on the night of the raid to expedite the unloading of supplies for the 'Battle of Monte Cassino' and was operating at full capacity.

On the afternoon of 2 December, a Luftwaffe crew made a reconnaissance flight over Bari in a Messerschmitt Me 210 twin-engined aeroplane, and the crew’s subsequent report led Generalfeldmarschall Albert Kesselring to order the raid. Kesselring and his staff had earlier considered Allied airfields at Foggia as the optimal targets, but the Luftwaffe lacked the resources for such an attack. von Richthofen, the commander of Luftflotte II, had suggested Bari as an alternative, for he believed that the crippling of this important port might slow the advance of General Sir Bernard Montgomery’s British 8^th Army and told Kesselring that the only aircraft available were his Ju 88A-4 bombers. von Richthofen thought that a raid by 150 Ju 88 bombers might be possible, but only 105 bombers were available, some of them from KG 54. Most of the aircraft were to fly from Italian airfields, but von Richthofen also wanted to deploy a few aircraft from Yugoslavia in the hope that the Allies might be fooled into thinking that the mission originated from there and misdirect any retaliatory strikes. The Ju 88 pilots were ordered to fly east to the Adriatic Sea, then swing south and west, since it was thought that the Allied forces would expect any attack to come from the north.

The attack began at 19.25, when two or three German aircraft circled the harbour at 9,845 ft (3000 m) dropping Düppel (foil strips) to confuse Allied radar. They also dropped flares, which were not in fact needed as the harbour was well illuminated. The German bomber force surprised the defenders and was able to bomb the harbour with great accuracy. Hits on two ammunition ships caused explosions which shattered windows 7 miles (11 km) away, and a bulk petrol pipeline on a quay was severed and the gushing fuel ignited, a sheet of burning fuel then spreading over much of the harbour and engulfing undamaged ships.

Some 28 merchant ships laden with more than 31,000 tons of cargo were sunk or destroyed, but three ships carrying another 6m,800 tons were later salvaged, and 12 more ships were damaged. The port was closed for three weeks and was restored to full operation only in February 1944.

One of the destroyed vessels, the 7,177-ton US Liberty ship John Harvey, had been carrying a secret cargo of 2,000 M47A1 mustard gas bombs, each holding some 60 to 70 lb (27 to 32 kg) of the agent. According to the Royal Navy’s official historian of World War II, the cargo had been sent to Europe for potential retaliatory use if Germany carried out its alleged threat to use chemical warfare in Italy. John Harvey's destruction caused liquid sulphur mustard from the bombs to spill into waters already contaminated by oil from the other damaged vessels. The many sailors who had abandoned their ships into the water became covered with the oily mixture, which provided an ideal solvent for the sulphur mustard. Some mustard evaporated and mingled with the clouds of smoke and flame. The wounded were pulled from the water and sent to medical facilities whose personnel knew nothing of the mustard gas and therefore concentrated their efforts on personnel with blast or fire injuries and therefore gave little attention to those merely covered with oil: many injuries caused by prolonged exposure to low concentrations of mustard might have been reduced by bathing or a change of clothes.

Within one day, the first symptoms of mustard poisoning had appeared in 628 patients and medical staff, these symptoms including blindness and chemical burns. That puzzling development was further complicated by the arrival of hundreds of Italian civilians who had been poisoned by a cloud of sulphur mustard vapour that had blown over the city. As the medical crisis worsened, little information was available about what was causing the symptoms, because the US military command wished to keep the presence of chemical munitions secret from the Germans. Nearly all of John Harvey's crew had been killed, and were thus unavailable to explain the cause of the 'garlic-like' smell noted by rescue personnel.

Informed about the mysterious symptoms, Deputy Surgeon General Fred Blesse sent for Lieutenant Colonel Stewart Francis Alexander, an expert in chemical warfare. Carefully tallying the locations of the victims at the time of the attack, Alexander traced the epicentre to John Harvey, and confirmed mustard gas as the responsible agent when he located a fragment of the casing of an M47A1 bomb.

By the end of the month, 83 of the 628 hospitalised military victims had died. The number of civilian casualties, thought to have been even greater, could not be accurately gauged since most had left the city to seek shelter with relatives.

An additional cause of contamination with mustard was suggested by the only survivor of the raid to have written about it. The huge explosion of John Harvey, possibly simultaneously with another ammunition ship, sent large amounts of oily water mixed with mustard into the air, and this then fell like rain on men who were on deck at the time. That affected the crews of the 'Hunt' class escort destroyers Zetland and Bicester. Both ships had been damaged by the blast and had taken casualties. After moving the destroyers away from burning ships and towing the tanker La Drome away from the fires, the ships received orders to sail for Taranto. They threaded their way past burning wrecks, with the flotilla leader, Bicester, having to follow Zetland as her navigation equipment was damaged. Some survivors were picked up from the water in the harbour entrance by Bicester. When dawn broke, it became clear that the magnetic and gyro compasses had acquired large errors, requiring a considerable course correction. Symptoms of mustard gas poisoning then began to appear. By the time the warships reached Taranto, none of Bicester's officers could see well enough to navigate the ship into harbour, so assistance had to be sought from the shore.

A member of General Dwight D. Eisenhower’s medical staff, Dr Stewart F. Alexander, was sent to Bari after the raid. Alexander had trained at the Army’s Edgewood Arsenal in Maryland, and was familiar with some of the effects of mustard gas. Although he was not informed of the cargo carried by John Harvey, and most victims suffered atypical symptoms caused by exposure to mustard diluted in water and oil, Alexander quickly came to the conclusion that mustard gas was present. Although he could get no acknowledgement from the chain of command, Alexander convinced the medical personnel to treat patients for mustard gas exposure and saved many lives as a result.

The Allied high command suppressed all news of the presence of mustard gas lest the Germans come to believe that the Allies were preparing to use chemical weapons and might react pre-emptively. The presence of many witnesses caused a re-evaluation of this stance, and in February 1944 the US chiefs-of-staff issued a statement admitting to the accident and emphasising that the USA had no intention of using chemical weapons except in retaliation.

Eisenhower approved Alexander’s report, but Winston Churchill, the British prime minister, ordered all British documents to be purged, and the attribution of mustard gas deaths to 'burns due to enemy action'.

An inquiry exonerated Coningham of negligence in defending the port, but found that the absence of previous air attacks had led to complacency.