The Dominican Civil War (Spanish: Guerra Civil Dominicana), also known as the April Revolution (Spanish: Revolución de Abril), took place between April 24, 1965, and September 3, 1965, in Santo Domingo, Dominican Republic. It started when civilian and military supporters of the overthrown democratically elected president Juan Bosch ousted the militarily-installed president Donald Reid Cabral from office. The second coup prompted General Elías Wessin y Wessin to organize elements of the military loyal to the dictator Reid ("loyalists"), initiating an armed campaign against the "constitutionalist" rebels.

Allegations of communist support for the rebels led to a United States invasion (codenamed Operation Power Pack), which later transformed into an Organization of American States occupation of the country by the Inter-American Peace Force. Although ostensibly neutral, U.S. civilian and military leaders deployed troops in a way that aided the anti-Bosch forces. Elections were held in 1966, in the aftermath of which Joaquín Balaguer was elected. Later in the same year, foreign troops departed from the country.

Juan Emilio Bosch Gaviño was the first democratically elected president of the Dominican Republic. Sworn into office on February 27, 1963, he tried to implement a number of social reforms, which caused the anger of the business magnates and members of the army, who initiated a rumor campaign that accused Bosch of being a communist. On September 25, 1963, a group of twenty-five senior military commanders, led by General Elías Wessin y Wessin, expelled Bosch from the country and installed Donald Reid Cabral as the new president. Reid failed to gather popular support, and several factions prepared to launch a counter-coup: Constitutionalists under Bosch, a group in the Dominican army under Peña Taveras, supporters of the former Dominican Revolutionary Party leader Nicolás Silfa and plotters siding with Joaquín Balaguer.

On April 24, 1965, three junior officers requested a meeting with President Donald Reid Cabral, who rejected the offer after he had received news of a suspected anti-government plot. When Chief of Staff Riviera Cuesta was instead sent to discuss with the officers at the August 16 military camp, he was immediately detained. A group of military constitutionalists and Dominican Revolutionary Party (DRP) supporters then seized the Radio Santo Domingo building and issued calls of sedition while Constitutionalist officers distributed weapons and Molotov cocktails to their civilian comrades. The transmissions prompted the garrison of the February 27 camp and a unit of the Dominican Navy's frogmen to defect. Large numbers of police officers abandoned their positions and changed into civilian clothing.

The following day, Reid appointed General Wessin y Wessin as the new chief of staff. Wessin rallied the government troops, branded them Loyalists, and announced his plans of suppressing the rebellion. At 10:30 am rebels stormed the presidential palace and arrested Reid. Several hours later, four Loyalist P-51 Mustangs conducted aerial bombings of the National Palace and other Constitutionalist positions, and one plane was shot down by ground machine-gun fire during the incident. A single Loyalist vessel, Mella, on the river Ozama, also bombarded the palace. Fearing that a mob, which had gathered at the palace, would lynch Reid, the rebel commander Francisco Caamaño allowed him to escape, as Reid had already lost the support of the Loyalists. The majority of the DRP leadership fled the capital, and Constitutionalists mobilized a total of 5,000 armed civilians and 1,500 members of the military. On April 26, José Rafael Molina Ureña was declared the provisional president, and large crowds gathered in the streets to demand Bosch's return from exile.

In the meantime, U.S. diplomats in Santo Domingo initiated preparations for evacuating 3,500 U.S. citizens. In the early morning of April 27, a group of 1,176 foreign civilians who had assembled in Hotel Embajador were airlifted to the Bajos de Haina naval facility, where they boarded USS Ruchamkin and USS Wood County, as well as the helicopters of HMM-264, which evacuated them from the island to USS Boxer and USS Raleigh. Later that day, 1,500 Loyalist troops, supported by armored cars and tanks, marched from the San Isidro Air Base, captured Duarte Bridge, and took position on the west bank of the Ozama River. A second force, consisting of 700 soldiers, left San Cristóbal and attacked the western suburbs of Santo Domingo. Wessin y Wessin ordered his armored units to cross the Duarte Bridge into Santo Domingo's center. However, the tanks quickly became bogged down in fierce combat within the narrow streets; armed civilians destroyed them. Unable to advance, the Loyalists retreated to San Isidro. The battle resulted in hundreds of casualties.

Rebels overran the Fortaleza Ozama police headquarters and took 700 prisoners. On April 28, armed civilians attacked the Villa Consuelo police station and executed all of the police officers who survived the initial skirmish. One U.S. Marine Corps battalion landed in Haina and later moved to Hotel Embajador, where it provided assistance in the upcoming airlifts. During the night, 684 civilians were airlifted to USS Boxer. One US Marine was killed by a rebel sniper during the operation. On April 29, the U.S. Ambassador to the Dominican Republic, William Tapley Bennett, who had sent numerous reports to U.S. President Lyndon Johnson, reported that the situation had reached life-threatening proportions for US citizens and that the rebels were Communists. Bennett stressed that the U.S. had to act immediately, as the creation of an international coalition would be time-consuming. Contrary to the suggestions of his advisers, Johnson authorized the transformation of evacuation operations into a large-scale military invasion through Operation Power Pack, which was aimed to prevent the development of what he saw as a second Cuban Revolution. It was the first overt U.S. military intervention in Latin America in more than 30 years, although it came on the heels of U.S.-backed coups in Guatemala and Brazil, as well as ongoing covert operations in Cuba.

At 2:16 a.m. on April 30, 1965, the 3rd Brigade of the 82nd Airborne Division landed at the San Isidro Air Base and started the U.S. military intervention in the conflict. During the next couple of hours, two brigade combat teams and heavy equipment were also dispatched. At sunrise the 1st Battalion, 508th Infantry Regiment moved up the San Isidoro highway under the cover of F-4 Phantom jets flying from Puerto Rico, securing a position east of the Duarte bridge. More units of the 82nd Airborne landed and secured the entire east bank of the Ozama River. Rebel positions across the river were destroyed by 105 mm howitzers. U.S. soldiers crossed the bridge and occupied a six-block area on the western side of the Duarte Bridge, but suffered casualties from sniper fire. The 1st Battalion 505th Infantry Regiment remained at the airbase and sent out patrols to the perimeter. A force of 1,700 Marines of the 6th Marine Expeditionary Unit occupied an area containing a number of foreign embassies. The locale was proclaimed an International Security Zone by the Organization of American States (OAS). Earlier in the day, the OAS also issued a resolution calling the combatants to end all hostilities. At 4:30 p.m., representatives of the loyalists, the rebels, and the U.S. military signed a ceasefire that was to take effect at 11:45 p.m. That timing favored the demoralized Loyalists, who had lost control of Ciudad Colonial.