Section 85H. The selectmen of a town and the prudential committee of a fire or water district may retire from active service any call fire fighter or reserve, special or intermittent police officer who becomes permanently disabled mentally or physically by injuries sustained through no fault of the person in the actual performance of duty as a fire fighter or police officer. A person so retired shall receive an annual pension equal to 2/3 of the annual rate of compensation payable to a regular or permanent member of the police or fire force, as the case may be, thereof for the first year of service therein and, if there are no permanent members of the police or fire force, an annual pension of $3000. If a call fire fighter or a member of a volunteer fire company in a town or a fire or water district whose service as such has been approved by the board of selectmen of the town or the prudential committee of a fire or water district or reserve or special or intermittent police officer of a town or a reserve police officer or reserve or call fire fighter of a city is disabled because of injury or incapacity sustained in the performance of the person's duty through no fault of the person and is thereby unable to perform the usual duties of the person's regular occupation at the time the injury or incapacity was incurred, the person shall receive from the city or town for the period of the injury or incapacity the amount of compensation payable to a permanent member of the police or fire force thereof, as the case may be, for the first year of service therein or, if there are no regular or permanent members of the police or fire force thereof, at the rate of $3000 per annum; provided, however, that no compensation shall be payable for any period after the police officer or fire fighter has been retired or pensioned in accordance with law or for any period after a physician designated by the board or officer authorized to appoint police officers or fire fighters in the city or town determines that the injury or incapacity no longer exists. All amounts payable under this section shall be paid at the same time and in the same manner as, and for all purposes shall be considered to be, the regular compensation of the police officer or fire fighter. No city, town or fire or water district shall pay compensation under this section if insurance providing coverage for the compensation is in effect therefor under any general or special law, unless and until all rights under the insurance in favor of the city, town or fire or water district shall have been exercised, determined and satisfied.