The aircraft carrying Władysław Sikorski, prime minister of the Polish government-in-exile, crashed off Gibraltar, killing him and fifteen others and leading to several conspiracy theories.

Władysław Eugeniusz Sikorski was a Polish military and political leader. Before World War I, Sikorski established and participated in several underground organizations that promoted the cause of Polish independence. He fought with distinction in the Polish Legions during World War I, and later in the newly created Polish Army during the Polish–Soviet War of 1919–1921. In the latter war, he played a prominent role in the decisive 1920 Battle of Warsaw.

The Polish government-in-exile, officially known as the Government of the Republic of Poland in exile, was the government in exile of Poland formed in the aftermath of the Invasion of Poland of September 1939, and the subsequent occupation of Poland by Germany, the Soviet Union, and the Slovak Republic, which brought to an end the Second Polish Republic.

On 4 July 1943, a Liberator II aircraft crashed off Gibraltar shortly after takeoff, killing all but one of the seventeen people on board. Among the victims were several senior Polish military leaders, including General Władysław Sikorski, the commander-in-chief of the Polish Army and prime minister of the Polish government-in-exile. The plane's pilot was the only survivor.

Władysław Sikorski's death controversy revolves around the death of the commander-in-chief of the Polish Army and Prime Minister of the Polish government in exile, General Władysław Sikorski, in the 1943 B-24 crash in Gibraltar. Sikorski's Liberator II crashed off Gibraltar almost immediately after takeoff, with the plane's pilot being the only survivor. The catastrophe, while officially classified as an accident, has led to several conspiracy theories that persist to this day, and often propose that the crash was an assassination, which has variously been blamed as a German, Soviet, British and even Polish conspiracy. The incident is still described by some historians as mysterious and was investigated by the Polish Institute of National Remembrance. They concluded that the injuries sustained were consistent with a plane crash and that there was not enough evidence to support or reject the theory that the plane was deliberately sabotaged.