Essex Police was the victim of 18 thefts from its own vehicles over a period of two years.
An electrical tracking device, stolen from a car parked in a public area in Braintree, was never recovered by officers.
The list of reported incidents includes the theft of a 16-seater minibus from the force’s headquarters in Chelmsford in May last year.
A Freedom of Information request revealed that items with a combined value of £26,691 were stolen in 2012 and 2013.
The tracking device, which was stolen from Braintree last April, was not found, but police were able to identify the culprits.
The minibus, valued at £20,000, was removed from Essex Police headquarters in Kingston Crescent, Chelmsford, overnight in May.
An Essex Police spokesman said: “The keys had been taken from a secure office by unknown means.
“It was driven a total of three miles and then returned to the HQ.”
Items worth more than £3,000, including mobile phones, cameras and cardboard cut-outs of policemen, have been stolen and not recovered.
The spokesman said: “Essex Police officers and staff are obviously very aware of the need to take steps to secure any property left unattended.
“The nature of policing does mean, though, that sometimes when responding to urgent incidents property security cannot be the main priority.
“While sensible crime prevention measures can help reduce the risks of theft they cannot eliminate them altogether and inevitably the force will occasionally become a victim itself.