As soon as the first news was received that a submarine campaign was
being conducted off the American coast, prompt action was taken by the
Navy Department. Destroyers, submarine chasers, and airplanes were sent
out in large numbers to patrol the coast and search the neighboring
waters, but the U-boat eluded detection. New York Harbor was
temporarily closed, and, though there was no indication of the presence
of hostile airplanes, the lighting of the city was for several nights
diminished by darkening the main thoroughfares. There were rumors that
the submarine either had a "mother ship" or was using a base on the
Mexican coast. Marine insurance rates were not raised, but the officers
of vessels in the coastwise trade were granted a bonus by the Shipping
Board.