Section 13D. Whoever commits an assault and battery upon any public employee when such person is engaged in the performance of his duties at the time of such assault and battery, shall be punished by imprisonment for not less than ninety days nor more than two and one-half years in a house of correction or by a fine of not less than five hundred nor more than five thousand dollars.

An officer authorized to make arrests may arrest any person upon probable cause and without a warrant if the person has committed an offense under this section upon a public employee when the public employee was operating a public transit vehicle and the officer may keep the person in custody during which period the officer shall seek the issuance of a complaint and request a bail determination with all reasonable promptness.

Whoever commits an offense under this section and which includes an attempt to disarm a police officer in the performance of the officer's duties shall be punished by imprisonment in the state prison for not more than 10 years or by a fine of not more than $1,000 and imprisonment in a jail or house of correction for not more than 21/2 years.

Whoever commits an assault and battery upon a police officer when such officer is engaged in the performance of the officer's duties at the time of such assault and battery and who by such assault and battery causes serious bodily injury to the officer shall be punished by a term of imprisonment in the state prison for not less than 1 year nor more than 10 years, or house of correction for not less than 1 year, nor more than 21/2 years. No sentence imposed pursuant to this section shall be for less than a mandatory minimum term of imprisonment of 1 year and a fine of not less than $500 nor more than $10,000 may be imposed but not in lieu of the mandatory minimum term of imprisonment. A prosecution commenced under this paragraph shall not be placed on file or continued without a finding and a sentence imposed upon a person convicted of violating this paragraph shall not be suspended or reduced, nor shall such person be eligible for probation, parole, work release, furlough or receive any deduction from the person's sentence for good conduct until such person shall have served said mandatory minimum term of imprisonment. For purposes of this section, the term ''serious bodily injury'' shall mean bodily injury which results in a permanent disfigurement, protracted loss or impairment of a bodily function, limb or organ or substantial risk of death.