Security was stepped up around the courthouse in the capital Freetown where the proceedings were later adjourned to Wednesday.
The 27 accused struggled to all squeeze onto the stand at the court-martial.
Justice Minister Mohamed Lamin Tarawalley was also present in the courtroom, according to the AFP journalist at the scene.
On November 26, armed attackers stormed a military armory, two barracks, two prisons and two police stations, clashing with security forces.
Twenty-one people were killed, and hundreds of prisoners escaped before authorities were able to regain control after what they deemed a coup attempt by members of the armed forces.
At least 80 people were arrested in connection with the clashes, most of them military personnel.
Former president Ernest Bai Koroma was charged last week with treason and other offences for his alleged role in the events.
Koroma’s case was adjourned until January 17.
Authorities have charged 12 other people with treason in connection with the coup attempt, including Amadu Koita, a former soldier and bodyguard of Koroma.
The violence in Sierra Leone at the end of November had sparked fears of another military coup in West Africa, where Mali, Burkina Faso, Niger and Guinea have all experienced putsches since 2020.
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