A Question About Brazilian Military Coup in 1964

[ralph124c]

In 1964, a group of Brazilian Army generals overthrew the president (Joao Goulart), and took over the government. The military ran the government for close to twenty years. when an elected government reemerged.
I have read that US president Lyndon Johnson was in contact with the rebel generals, and despatched a naval task force to Brazil-consisting of an aircraft carrier and four destroyers. my question: assuming that some generals would be loyal to Goulart, then there would have been a civil war. What could the US forces have accomplished? Did Johnson give the task force any orders?
Frankly, intervening in a country as vast as Brazil would seem to be asking for trouble.
Have any of the documents relating to this been declassified?

[Measure_for_Measure]

Wikipedia has links:

1964 Brazilian coup d'état

National Security Archive has documents:

Brazil Marks 40th Anniversary of Military Coup

The last link refers to arms being supplied covertly:

To assure the success of the coup, Gordon recommended “that measures be taken soonest to prepare for a clandestine delivery of arms of non-US origin, to be made available to Castello Branco supporters in Sao Paulo.” In a subsequent cable, declassified just last month, Gordon suggested that these weapons be “pre-positioned prior any outbreak of violence,” to be used by paramilitary units and “friendly military against hostile military if necessary.” To conceal the U.S. role, Gordon recommended the arms be delivered via “unmarked submarine to be off-loaded at night in isolated shore spots in state of Sao Paulo south of Santos.”