Coast Guard and Brevard County sheriff's officers spent two hours searching the ship Thursday before determining the threat was a hoax.
"We did a sweep in accordance with security procedure," said Coast Guard Lt. Carol Swinson.
The call about the cruise ship Sensation reached the Coast Guard Thursday afternoon. After the search, the passengers reboarded, and the ship left port shortly after 8 p.m.
Carnival's Web site shows Sensation has a passenger capacity of 2,052 and a total crew of 920.
The company released a statement about the incident saying, "Carnival Cruise Lines takes any security threat very seriously and is working with law enforcement officials as the investigation continues."
The discovery of the submarine has unveiled a few "inconsistencies." For example, how can one explain the fact that the sub was found where it needed to be searched for from the start?