[ad_1] A former United States ambassador accused of working for decades as a secret agent for Cuba in one of the biggest national security breaches in years pleaded guilty on Friday and was sentenced to 15 years in prison. Manuel Rocha, 73, pleaded guilty to two charges — conspiring to defraud the United States as a foreign agent and failing to register as a foreign agent — as part of an agreement with the federal government. He also faces three years of supervised release, and a $500,000 fine. Mr. Rocha,…