The ABC was a Cuban political organization founded in 1931 in opposition to the government of Gerardo Machado. It used a hierarchy of clandestine cells, in which each member would oversee a cell on the next level. The first cell was labeled A; the next tier B; then C, and so forth.
The ABC gained prominence quickly through dissemination of propaganda and through acts of terrorism. The group accepted the invitation of US Ambassador Sumner Welles to participate in a new government, only to be forced out of power in less than a month, becoming again an opposition group during the One Hundred Days Government.
The ABC was founded in October 1931 by a group that had been meeting for a year in the office of Dr. Juan Andrés Lliteras. The most prominent member was Joaquín Martínez Saenz. Jorge Mañach and Francisco Ichaso were soon invited to join. The group's membership was predominantly middle class, including students and professionals.
Cells had about seven members, each of whom could lead a cell on the tier below. Members of the organization knew only their leader and the cell below them. The system of alphabetical lettering of cells from tier to tier gave the organization its name.
A sequence of numbers along with the letter identified each individual member. The members of cell A were numbered A1, A2, A3, etc. They gave their number as the first digit used in the next cell; the cell led by A3 would have members B31, B32, B33, etc.
The organization took credit for numerous terrorist attacks like assassinations and bombings. They targeted police officers and soldiers, and also made several high-profile killings, including Senate President Clemente Vázquez Bello. The ABC reportedly orchestrated a plan to kill Machado by bombing Vazequez Bello’s funeral, but failed due to a last-minute change of cemetery.
In early 1932 the government created a secret police force called the Porra, which acted against the opposition with no less violence. This repression further weakened the Machado government and enhanced the ABC's standing.
The ABC maintained close contact with Cuba's radical student group, the Directorio Estudiantil Universitario. Student leader Eduardo Chibás wrote that students sometimes carried out the bombing missions, with the ABC providing funding and equipment, and also taking credit.