By Gideon Long

                                    LONDON (Reuters) - The failure of the U.S.-backed Bay of Pigs invasion of
                                    Cuba in 1961 was due in part to "intense internal jealousies" within the CIA,
                                    British documents released Wednesday claimed.

                                    The documents, regarded as secret until now, are scathing about the Defense
                                    Department's preparation for the invasion, which heightened tension between
                                    the United States and the fledgling regime of Cuban leader Fidel Castro.

                                    In April 1961, around 1,500 opponents of Castro launched a surprise attack on
                                    Cuba in a bid to topple the government. The invasion was a fiasco and was
                                    easily repelled.

                                    A month later, an aide to U.S. President John F. Kennedy came to London to
                                    brief the British Foreign Office on what had gone wrong. The Foreign Office
                                    forwarded information from the briefing to British Prime Minister Harold
                                    Macmillan.

                                    "The intelligence failure of the CIA appears explicable only on the assumption of
                                    intense internal jealousies..," Foreign Office official H.A.A. Hankey writes in a
                                    letter to Tim Bligh, Macmillan's principal private secretary.

                                    "The Department of Defense also seems to have failed to
                                    consider the most elementary point -- where to invade," continues the letter,
                                    dated May 5, 1961, and released by Britain's Public Record Office (PRO).

                                    "They really could hardly have chosen a worse point," it says.

                                    Another letter, also from May 1961, suggests Kennedy's faith in the U.S.
                                    intelligence service was shattered by the Bay of Pigs debacle.

                                    "The President has certainly lost confidence in the CIA," David Ormsby Gore,
                                    Britain's ambassador to Washington, writes to Bligh.

                                    "The American public was in a mood of extreme frustration (following the
                                    botched invasion) and the President had felt it necessary to make some rousing
                                    speeches ..."

                                    Earlier correspondence between Macmillan and Kennedy's predecessor
                                    Eisenhower suggests Britain felt it had been left in the dark over U.S. policy
                                    toward Cuba.

                                    Eisenhower wrote to Macmillan in July 1960 to ask for Britain's support in
                                    isolating Castro, who was forming ever-closer ties with the Soviet Union.

                                    In his reply, Macmillan agrees that the Cuban leader "is really the very devil" but
                                    says he needs more information.

                                    "It would ... make it easier for us to help if we had a rather clearer
                                    understanding of your actual intentions," Macmillan writes. "I am not very clear
                                    how you really mean to achieve this aim."

                                    The Bay of Pigs fiasco heightened Cold War tensions and marked the start of
                                    40 years of animosity between Cuba and the United States.

                                    It foreshadowed the Cuban Missile Crisis of a year later, which some analysts
                                    still regard as the closest the world has come to nuclear war.

                                    With hindsight, one memo from the British Foreign office to its ambassador in
                                    Washington in 1960 appears particularly prophetic.

                                    "The greatest danger, which must be avoided at all costs, is an unsuccessful
                                    operation that would leave Castro in power but more embittered than ever," it
                                    reads.