(covers information from several alternate timelines)
An aircraft carrier was a type of naval warship in Earth's 20th and 21st century. Its design and size allowed for aircraft, including fighters, bombers, and helicopters, to be launched and retrieved at sea. It was characterized by a long, flat "flight deck" which served as a mobile air base, condensing apron, landing strip, and runway into a small space. Many aircraft carriers after World War II were powered by nuclear fission.
In an alternate 1944, during World War II, the San Francisco Bay was home to aircraft carriers. As Shuttlepod 1 flew into the bay, one aircraft carrier was entering the bay, while the other was anchored near Yerba Buena Island. Later, in New York City, Alicia Travers mistook a statement by Jonathan Archer, thinking he had served on the USS Enterprise (CV-6). (ENT: "Storm Front")
When the crew of the destroyed USS Enterprise (NCC-1701) traveled back in time to the year 1986, they collected nuclear radiation from the reactor of the USS Enterprise (CNV-65). This enabled them to recrystallize the dilithium of their captured Klingon Bird-of-Prey. (Star Trek IV: The Voyage Home)