It was more atonal and twelve tone.

The Rapid Deployment Infantry Battalions (BIRI), specialized in anti guerrilla warfare, also began to be created (Atlacatl March 1981, Atonal January 1982, Belloso May 1982, etc.).

However, according to statements made to the Commission on the Truth by officers stationed at the El Paraíso barracks at the time, a meeting was held in which officers of the General Staff of the Fourth Brigade, including its Commander, Colonel Mario A. Reyes Mena, and officers of the Atonal Rapid Deployment Infantry Battalion (BIRI) took part.