West Midlands police officers sustained facial injuries when a brick was hurled from a Coventry bridge at the police car they were in.
A 49-year-old police sergeant and a 27-year-old police constable, both men, were taken to hospital and treated for their injuries.
The pair were responding to an emergency call at around 11.40pm on Sunday, 15 February, and were driving along the city's ring road when a coping stone was hurled from a bridge, smashing the windscreen.
Police believe the car was targeted by the culprits and that the officers were lucky not to sustain more serious injuries.
Detective Inspector Stuart Bell, from the force's Criminal Investigation Department, said: "The officers who between them have over 30 years' service were on their way to an emergency call when we believe two people deliberately targeted a police car.
"Fortunately the officers are not seriously hurt − it is by pure luck that we are not dealing with a more serious incident.
"Not only did the mindless action of these people cause police officers having to spend a night in hospital but it also meant that someone who desperately needed our help and had dialled 999 was left vulnerable.
"I am sure someone out there knows who did this and I am appealing to anyone with any knowledge of the people involved to come forward and to call the police.
"Both men have now been released from hospital and are spending time with their families as they continue to recover from this incident."
Anyone with information is urged to call Coventry police on 101. Alternatively people can leave information anonymously by calling Crimestoppers the independent charity on 0800 555 111.