At the center of Santos' backlash against the military's top brass, widely seen to be above the law, are numerous reported irregularities in defense procurement and extrajudicial killings.
Santos said he had to act in "a clear, forceful way" against both foreign and internal enemies of state institutions, including those seen to be enriching themselves or allowing corruption.
Colombia's nascent defense industry is said to be neglected because of defense procurement officials' eagerness to profit from foreign purchases.
Opposition critics and Colombian news media frequently cited the problems that hindered growth of a domestic defense industry, corruption in defense procurement and the military's involvement in summary executions.
Santos fired the armed forces commander, Gen. Leonardo Barrero, and an unspecified number of other senior officers implicated in hundreds of hours of recorded conversations quoted by Semana news weekly. The conversation records were cited by Semana in an exposure of corruption in military procurement.
Some of the officers implicated in the scandal have already left the country.
Defense Minister Juan Carlos Pinzon acknowledged "administrative deficiencies" in 10 army procurement contracts and cited the collection of kickbacks of up to 50 percent of the value of procurement transactions.
Pinzon said the army's inspector-general, Gen. Ernesto Maldonado, randomly selected 105 contracts for close examination and detected irregularities in 10 of them.
Future defense procurement will be handled by the Defense Ministry and outside auditors will be brought in, he said.
The military's rule in extrajudicial killings was also a factor in some of the dismissals, although government officials focused on the anti-corruption campaign.
A Colombia Defense and Security Report by Business Monitor International said the government still needs to resolve issues related to its ongoing talks on ending a military confrontation with guerrilla organizations Revolutionary Armed Forces of Colombia and National Liberation Army.
Conflict between the rebel groups and successive governments in Bogota has been a major reason behind military procurement worth tens of millions of dollars.
Meanwhile, El Tiempo newspaper said fresh findings by Colombia and U.S. law enforcement agencies had found evidence of close links between Latin American guerrilla movements and the Russian and Italian organized crime organizations that were active not only in Colombia, but also in Ecuador, Honduras and Peru.