Section 18. Whoever, in the night time, enters a dwelling house without breaking, or breaks and enters in the day time a building, ship or motor vehicle or vessel, with intent to commit a felony, no person lawfully therein being put in fear, shall be punished by imprisonment in the state prison for not more than ten years or by a fine of not more than five hundred dollars and imprisonment in jail for not more than two years. Whoever commits any offense described in this section while armed with a firearm, rifle, shotgun, machine gun or assault weapon shall be punished by imprisonment in the state prison for not less than 7 years or by imprisonment in the house of correction for not less than 2 years nor more than 21/2 years.