Inspectors at Chelmsford Prison have warned it is understaffed and becoming increasingly violent - with a sharp rise in the number of assaults against both officers and other inmates.
The Independent Monitoring Board has published its latest report, in which it also raises big concerns about drug trafficking, poor mental health support and bullying.
The board says between September 2016 and August this year, staffing levels "fell well below the benchmark figure" - even when that benchmark was reduced temporarily.
"The prison’s ability to control the influx of drugs and other contraband, and to maintain discipline, has been hampered by the shortfall in the number of officers available for much of the reporting period, and the lack of experience of many of the newer officers."
Figures from the Ministry of Justice show the number of assaults, including fights, at HMP Chelmsford rose from 162 in 2012 to 414 in 2016.
During that time, the number of "prisoner on prisoner" attacks more than doubled while assaults on prison staff increased by 400%.
In the year from September 2016, three inmates killed themselves.
"It is our view that the widespread availability of drugs, despite the best efforts of the prison to detect them and to prevent their use, and of bullying, often as a result of prisoner indebtedness, are primary causes of the reported violence, prisoner injuries and self-harm."
The damning report says it fears the Category B prison is acting simply as a "warehouse" for inmates ad fails to point them in a more positive direction.
However it also praises officers' professionalism, saying they "have shown great commitment to their work while under great pressure".