Section 85E. The appropriate retirement board, established under section twenty, or, if there is no such board, the selectmen of every town which has accepted this section shall retire from active service:

(a) Any permanent member of the police department and any permanent member of the fire department of such town who becomes permanently disabled, mentally or physically, by injuries sustained through no fault of his own in the actual performance of duty, from further performing duty as such member.

(b) Any permanent member of either of said departments who has performed faithful service therein for not less than twenty years continuously and becomes permanently incapacitated for further duty as such member before attaining the age of sixty.

(c) Any permanent member of either of said departments, at his request, at any time after attaining the age of sixty and before attaining the age of sixty-five, if he has performed faithful service therein for not less than twenty years continuously.

(d) Any permanent member of either of said departments on attaining the age of sixty-five without any request on his part. No permanent member of either of said departments shall remain in service after he has attained or shall attain the age of sixty-five.

If a permanent member of a police department of such a town was, prior to the establishment of a police department therein, employed in said town as a police officer by appointment under section ninety-six of chapter forty-one, the period of such appointment shall be counted as a part of his continuous service as a permanent member of its police department.

Any member of either of said departments retired under the provisions of subdivision (a) of this section shall receive an annual pension equal to seventy-two per cent of the highest annual rate of compensation received by him while holding the grade held by him at the time of his retirement. Any member of either of said departments retired under the provisions of subdivision (b), (c) or (d) of this section shall receive an annual pension equal to sixty per cent of the highest annual rate of compensation received by him while holding the grade held by him at the time of his retirement if he has completed twenty years of service, and an additional amount equal to one per cent for each year of service after the first twenty; provided, that the total amount of such pension shall in no case exceed seventy-two per cent of said compensation.

The selectmen may in an emergency call upon any person so pensioned for such temporary service in the department from which he was retired as they may deem him fitted to perform, and during such service he shall be entitled to be paid the difference between the rate of full pay for such employment and the rate of pension received by him.

No police officer or fireman whose employment began after June thirtieth, nineteen hundred and thirty-seven shall be subject to the provisions of this section.

The provisions of section eighty-five, or of any special law authorizing the granting of non-contributory pensions to members of the police department or the fire department, as the case may be, of a town which accepts this section shall no longer apply thereto.