On the earlier (non-turreted) version, for example, the Boston III, the pilot bailed out before the rear crew, contrary to SOP on most other aircraft.
The rear gunner / radio compartment was fitted with rudimentary flight controls (i.e stick and rudder pedals), and it was the gunner's job to hold the aircraft steady whilst the pilot exited the cockpit, and slid off the wing. The gunner could then exit via the floor hatch, or "over the side".
For emergency exit on the ground, the nose compartment was fitted with an escape hatch panel on the port side of the glazing ( entrance hatch in floor used for bail out). Pilot and rear crew used the cockpit roof hatch and the open gun position respectively (upper escape hatch on turreted versions).