Final answer:
The partial blackout was due to a power outage, as part of World War II emergency protocols to prevent enemy forces from detecting targets during air raid drills.
Step-by-step explanation:
The city was in a partial blackout due to a power outage that was part of an emergency protocol established by the Office of Civilian Defense during World War II. To prevent enemy forces from identifying targets by their lights at night, civilians on the coast and in other vulnerable areas were instructed to eliminate all visible light during air raid drills. These blackout procedures included covering windows and turning off streetlights, with the air raid wardens patrolling to ensure compliance. To simulate the conditions of an actual enemy attack, they included scheduled power outages, essentially causing the partial blackout.