Section 83A. In cities, except Boston, which have accepted this section by vote of the city council, subject to the provisions of the city charter, the appropriate retirement board, established under section twenty, shall retire from active service:

(a) Any member of the police department of such city 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 said department 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 said department, at his request, at any time after attaining the age of fifty-five 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 said department on attaining the age of sixty-five without any request on his part. No permanent member of said department shall remain in service after he has attained or shall attain the age of sixty-five.

Any member of said department 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 said department 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 retirement, if he has completed twenty years of service, and an additional amount equal to one per cent of said annual compensation 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 annual compensation.

The board of police, or the mayors in cities having no such board, may in an emergency call upon any person so pensioned for such temporary service in the department as he may be 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-three, or of any special law authorizing the granting of non-contributory pensions to members of the police department thereof, shall no longer apply to any city which accepts this section.