Criminals are escaping arrest because police are delayed in getting to crime scenes in patrol cars that do not have sirens, officers have warned.
Police "fear letting down the public" because they are being sent to urgent calls in the ill-equipped cars, which have been ordered as part of cost cutting measures, a union has warned.
The West Midlands Police Federation, which represents rank and file officers, said they are being hampered by the lack of proper resources.
The Force has a fleet of 109 of the Vauxhall Corsa patrol cars which were originally intended for neighbourhood policing and non-urgent incidents.
But the Federation said they are being used in emergencies due to staff cuts.
It said there have been more than 100 reports in the past 12 months of police attending urgent incidents in the West Midlands in cars without the "blues and twos".
The Federation's health and safety chief Pete Harkness said: "Officers are ordered to drive the Corsa at patrol speed and obey the rules of the road.
"But the absence of a siren means they often cannot get traffic to move out of their way and this, in turn, can delay them getting to an emergency situation.
"This is very frustrating for the officers and they feel they are letting the public down by not getting to them as quickly as possible in a crisis situation."
The Federation's deputy chairman, Tom Cuddeford said: "We know there is a lot of concern about this among our officers.
"They want to protect the public and catch criminals. But they get frustrated when they are not provided with the tools to do the job effectively because that impacts on the service they can provide to members of the communities they serve."
Superintendent Kerry Blakeman, from the Force's operations department, said officers who respond to call-outs in cars without sirens have to follow the Highway Code, and so cannot break the speed limit to cut through traffic.
Mr Blakeman said: "Incidents graded as 'immediate' are responded to as soon as possible, usually in a matter of minutes and on many occasions require the use of lights and sirens.
"At no point was the Corsa intended for response work as it is a low performance vehicle."