Castro gathered 165 revolutionaries for the mission, ordering his troops not to cause bloodshed unless they met armed resistance. The attack took place on 26 July 1953, but ran into trouble; 3 of the 16 cars that had set out from Santiago failed to get there. Reaching the barracks, the alarm was raised, with most of the rebels pinned down by machine gun fire. Four were killed before Castro ordered a retreat. The rebels suffered 6 fatalities and 15 other casualties, whilst the army suffered 19 dead and 27 wounded. Meanwhile, some rebels took over a civilian hospital; subsequently stormed by government soldiers, the rebels were rounded up, tortured and 22 were executed without trial.
Castro was sentenced on 16 October, during which he delivered a speech that would have been printed under the title of History Will Absolve Me. Castro was sent to 15 years' imprisonment in the hospital wing of the Model Prison (Presidio Modelo), a relatively comfortable and modern.