Operation Brother Sam was the use of the United States Navy and Air Force in support of the coup in Brazil in 1964. With the deterioration in relations with João Goulart's government and the favorable attitude of the groups conspiring against him, the idea of an operation to ensure the success of an uprising arose. The issue was discussed between the U.S. ambassador to Brazil, Lincoln Gordon, and officials in Washington throughout the administration of president John F. Kennedy and his successor Lyndon B. Johnson. They thought about logistical support, the positioning of a squadron on the Brazilian coast to "show the flag" and even, in an extreme situation, a plan for a gigantic land operation, which was not used. The operation was planned by maintaining contact with Brazilian conspirators such as general Castelo Branco, and had as an assumption the formation of a provisional government that would request foreign aid.

With the outbreak of the coup d'état, the operation was activated to transfer fuel such as gasoline by sea to the insurgent military, to leave a squadron near Brazil, and to take war supplies by air. The naval component consisted of the aircraft carrier USS Forrestal, a helicopter carrier and six destroyers from the Second Fleet, as well as four tankers. The aircraft carrier departed from Virginia, while the tankers were to load in the Caribbean. The air component was seven C-135 aircraft, eight supply aircraft, one air support and rescue aircraft, eight fighters, a communications plane, an airborne command post, weapons and ammunition. Air Force general George S. Brown was given command of the mission, which was coordinated by the Southern Command in Panama.

While shipments waited at the air bases, ships began to leave their ports. However, the opposition military in Brazil quickly overthrew the Goulart government, and Castelo Branco reported that logistical support would not be needed. The operation was thus deactivated before it had any physical effect in Brazil, but it demonstrated the interventionist disposition of the American government. It came to light between 1976 and 1977 with the declassification of documents.

After the Cuban Revolution in 1959, the U.S. government's attitude toward leftist leaders in Latin America hardened. Among them was the government of João Goulart in Brazil. The United States was worried by Goulart's domestic and foreign policies and bilateral relations deteriorated. As the Alliance for Progress failed to influence him with moderate methods, Washington resorted to weakening the Brazilian government with measures such as financing the opposition's electoral campaigns in 1962 and redirecting economic assistance to opposition governors.

After a certain period, disputed in the literature, Washington became favorable to the ousting of Goulart. Since 1961 some groups in the Brazilian military were conspiring against the government, and the U.S. Embassy was aware of such movements. By 1963 the U.S. government was already looking for a group in the Brazilian Armed Forces capable of overthrowing Goulart. Meanwhile, by the end of that year it was developing contingency plans and working on what to do in case of a rebellion. A concern arose that the rebels would need American support to succeed; on October 7, Kennedy asked Gordon about the possibility that intervention might be necessary. A State Department document made in November mentioned a new contingency plan with "heavy emphasis on armed U.S. intervention." The contingency plan that would lead to operation Brother Sam had a wider scope than the operation itself.

The December 11, 1963 version of the contingency plan, probably in development since the previous months, listed four possibilities. The third, the removal of Goulart, was similar to what actually happened. The second was:

Overt, organized resistance by sizable democratic forces, with considerable military support, against Goulart effort to seize authoritarian power.

This implies the possibility of civil war or at least a clash between democratic forces and the incumbent Goulart regime. In such circumstance we should carefully abstain from giving support to Goulart by public pronouncement, by arms supply, or in any other way. We should maintain an initial non-interventionist posture but at the same time seek ways and means of assisting the democratic forces.