Hovering helicopters, Coast Guard boats and Maine Marine Patrol vessels will descend on Casco Bay tomorrow for a major oil-spill response drill.

As many as 1,000 emergency workers are expected to take part in the two-day drill that will be visible most of the morning from the Eastern Prom in Portland.

They will respond to an imaginary car carrier and an oil tanker crash in a strong winter storm, marked by frigid temperatures and limited visibility, somewhere 16 miles out in the Gulf of Maine.