Upvote:11
There was a lot of rapidly changing technology in the B-29's guns during the lifetime of the aircraft, and hence a lot of change in nomenclature for different crew roles. It seems that EMG was used at the end of the war for "Electrical Mechanical Gunner", as seen in crew rosters such as the ones given here in spelled out form, and here in abbreviation. More precisely, "Airplane Electrical Mechanic-Gunner" was "Military Occupational Specialty" 1685, which a militaria site (no doubt based on WWII-era publications; see also this) describes as
AIRPLANE ELECTRICAL MECHANIC-GUNNER (1685) Inspects and makes repairs to aircraft electrical equipment excluding radio transmitters and receivers and aircraft instruments. Fires aerial machine guns on combat missions.
Examines electric wiring, auxiliary electric motors, ignition systems, and lighting units for proper functioning. Uses a combination electrical continuity tester or ohmmeter, ammeter, and voltmeter to locate short circuits and to test currents and resistances. Traces circuits with aid of blueprints. Tightens and solders loose electrical connections. Cleans, repairs, and replaces electric motors, ignition units, recognition and landing lighting units, relays, junction boxes, and other related equipment.
Uses such tools as screw drivers,wrenches,wire cutters, ο¬le,and pliers. Must be familiar with aircraft electrical systems and with basic electrical theory. Must be able to read blueprints.
There is a 1947 report on the aptitude testing & training for this MOS, which makes interesting reading.
T.E.D. points out, in a comment, that this technology is described in a recent article. Another is here. Together these might give an idea of the setting of your grandfather's B-29 experience.
So this job entailed maintaining and using the analog computers used for remote fire control of the gun turrets. I would assume that as new equipment was installed in an B-29 some fraction of gunners would take a special course on its maintenance, and EMG was the job title for a gunner with this extra training. Being a gunner entailed both video-game-like point & shoot aspects during combat, and maintenance and service of the equipment all the rest of the time.