The Cuban Air Force shot down two unarmed aircraft owned and operated by Brothers to the Rescue, an anti-Castro exile group that aids help Cubans who want to come to the United States.
The group had repeatedly entered Cuban airspace in the past several years. Violating a country's air space is tantamount to to violating its national sovereignty. The organization's planes had further antagonized Cuba by dropping anti-Castro leaflets and flying by buildings in Havana.
The last time they did it, two of the planes entered Cuban airspace. The other plane with the groupís head, Josť Basulto, who was part of the Bay of Pigs invasion and fired a canon on a Cuban hotel a year later, made it back to Cuba safely.
All of the planes were repeatedly warned to leave Cuban airspace, but flew on anyway. Eventually Cuban MiGs entered the air and downed two of the three planes, killing all on board.
The group, and American lawmakers, were outraged at the attack because the planes were unarmed and at the time they were shot down, the US claims they had reached international waters.
The planes were also civilian aircraft and entirely unarmed. The US had considered a military retaliation, but decided against it. The United Nations has condemned Cuba's action.  The U.S. later passed the Helms-Burton act, tightening the blockade against Cuba.