Devon and Cornwall Police has been put into special measures by the police inspectorate after failures in recording and responding to crime.
The watchdog found three areas of improvement that the force must make; response to emergency calls, recording of crime and management of registered sex and violent offenders.
The force says it has already begun to make improvements to its service since the initial inspection in January.
In a statement, it says it has 'accepted' the findings and understands how they may cause concern in the community.
Temporary Chief Constable of Devon and Cornwall Police, Jim Colwell said "We are committed to delivering improvements.
“Whilst there are improvements we must make; I am extremely proud that Devon and Cornwall remain the second safest counties in the country and this is a testament to the hard work of all our officers, staff and volunteers. Protecting victims of crime remains our priority as we strive to meet our mission for world-class policing and to provide the best possible service for our communities.
“We take these findings very seriously and we will continue to work closely with HMICFRS, our key partners and our Police and Crime Commissioner, Alison Hernandez, to embed sustainable improvements in the areas identified. We remain committed to delivering the excellent policing service our communities deserve.”
His Majesty's Inspectorate of Constabulary and Fire & Rescue Services (HMICFRS) will now monitor the Force under its enhanced Engage process which provides additional scrutiny and support on behalf of the public.
The monitoring process consists of two stages: Scan and Engage. All police forces are in the Scan phase by default but can be escalated to Engage if failings are identified.
The watchdog detailed the reasons it had decided to move Devon and Cornwall Police into the engage phase because its crime recording had 'deteriorated' since its last inspection.
They went on to say that the force 'doesn’t always record crimes against vulnerable victims, particularly violent or behavioural crimes, and anti-social behaviour.'
HMICFRS also said the force did not answer, or respond to, emergency or non-emergency calls within adequate timeframes, and too many calls were abandoned.
Identification of repeat and vulnerable callers was missed, and callers were not always given the appropriate advice on the preservation of evidence or crime prevention, the inspectorate found.
The police inspectorate also found the force was unable to adequately manage registered sexual and violent offenders, which it said meant an increased risk of further offending may not be identified.
His Majesty’s Inspector of Constabulary Wendy Williams said: “We move police forces into our enhanced level of monitoring, known as Engage when a force is not responding to our concerns, or if it is not managing, mitigating or eradicating these concerns. The Engage process provides additional scrutiny and support.
“Devon and Cornwall Police has been asked to urgently produce an improvement plan and will meet regularly with our inspectors. We will work closely with the force to monitor its progress against these important and necessary changes.”
HMICFRS says that its next inspection report is due to be published early next year.