Two prison officers were taken to hospital with serious injuries after young inmates rioted at a Staffordshire jail.
Details of the riot at Swinfen Hall prison near Lichfield, Staffordshire, on Thursday have only just emerged.
The jail houses 600 long-term young men serving sentences from four years to life.
It has a recent history of disturbances, including a riot in August when four prisoners were injured and a fire broke out.
The jail was locked down while fire, ambulance and specialist warders dealt with the trouble.
In the latest disturbance one prison officer suffered a suspected broken jaw, while another had head and face injuries.
Others suffered cuts and bruises.