Churchill arranged for Townsend's assignment as air attaché at the British Embassy in Brussels; he was sent on 15 July 1953, before Margaret's return from Rhodesia on 30 July. The assignment was so sudden that the British ambassador learned about it from a newspaper. Although the princess and Townsend knew about his new job, they had reportedly been promised a few days together before his departure.
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.