[6] Richthofen believed that crippling the port might slow the advance of the British Eighth Army and told Kesselring that the only aircraft available were his Junkers Ju 88A-4 bombers.

[7] Most of the aeroplanes were to fly from Italian airfields but Richthofen wanted to use a few 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 opened at 19:25, when two or three German aircraft circled the harbour at 10,000 ft (3,000 m) dropping Düppel (foil strips) to confuse Allied radar.

One of the destroyed vessels—the US Liberty ship John Harvey—had been carrying a secret cargo of 2000 M47A1 mustard gas bombs, each holding 60–70 lb (27–32 kg) of the agent.

According to Royal Navy historian Stephen Roskill, the cargo had been sent to Europe for potential retaliatory use if Germany carried out its alleged threat to use chemical warfare in Italy.

[8] The destruction of John Harvey caused liquid sulfur mustard from the bombs to spill into waters already contaminated by oil from the other damaged vessels.

That puzzling development was further complicated by the arrival of hundreds of Italian civilians also seeking treatment, who had been poisoned by a cloud of sulfur mustard vapor that had blown over the city when some of John Harvey's cargo exploded.

As the medical crisis worsened, little information was available about what was causing the symptoms, because the US military command wanted to keep the presence of chemical munitions secret from the Germans.

[27] Informed about the mysterious symptoms, Deputy Surgeon General Fred Blesse sent for Lieutenant Colonel Stewart Francis Alexander, an expert in chemical warfare.

The huge explosion of John Harvey, possibly simultaneously with another ammunition ship, sent large amounts of oily water mixed with mustard into the air, which fell down like rain on men who were on deck at the time.

[30] A member of Allied Supreme Commander General Dwight D. Eisenhower's medical staff, Dr. Stewart F. Alexander, was dispatched to Bari following the raid.

The presence of multiple 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 emphasizing that the US had no intention of using chemical weapons except in the case of retaliation.

[33] In 1988, through the efforts of Nick T. Spark and US Senators Dennis DeConcini and Bill Bradley, Alexander received recognition from the Surgeon General of the United States Army for his actions in the aftermath of the Bari disaster.

[35] In his autobiographical work Destroyer Captain, published in 1975 by William Kimber & Co., Lieutenant Commander Roger Hill describes refuelling HMS Grenville in Bari shortly after the attack.

[citation needed] An inquiry exonerated Sir Arthur Coningham of negligence in defending the port but found that the absence of previous air attacks had led to complacency.