The bay of pigs invasion failed when a. the soviet union intervened to protect the castro government. b. anti-castro cubans in florida refused to support the effort. c. president kennedy's use of u. s. air power led to the capture of american pilots. d. the anti-castro exiles were defeated by the cuban military. e. the cuban rebel forces lost the battle of havana

D.  The anti-Castro exiles were defeated by the Cuban military.

Within just three days in April, 1961, the force of exiles invading at the Bay of Pigs was soundly defeated by the Cuban Revolutionary Armed Forces, commanded by Cuba's communist leader Fidel Castro.   The Cuban exiles whom mounted the invasion had been trained by the USA's Central Intelligence Agency, and were attempting to overthrow Castro's government.In the aftermath of the Bay of Pigs affair, Cuba requested that the USSR, as its communist sponsor, place missiles in Cuba to deter further US-sponsored action against the Castro regime.  That request, coupled with the fact of American missiles that were located in Europe, within striking distance of the USSR, prompted Nikita Khrushchev of the USSR to send the missiles to Cuba.  And that became the "Cuban Missile Crisis" of 1962. 

(d) it was complex and capable of highly organized efforts.