The A4W designation stands for:
- A = Aircraft carrier platform
- 4 = Contractor's fourth core design generation
- W = Westinghouse, the contracted designer
These nuclear fission pressurized water reactors (PWRs) were jointly designed by Bettis Atomic Power Laboratory and Knolls Atomic Power Laboratory and built by Westinghouse Electric Company. Their reactor cores are expected to operate for about 20 years before refueling is required. The only ships to use these nuclear reactors are the Nimitz class supercarriers, which have two reactors rated at 550 MWth each. These generate enough steam to produce approximately 100 MW of electricity, plus 140,000 shaft horsepower (104 MW) for each of the ship's four shafts – two per propulsion plant.
- "A4W". US Navy Propulsion Systems. Federation of American Scientists. 1999-02-27. Archived from the original on 25 September 2006. Retrieved 2006-10-16.
current cores for the NIMITZ Class aircraft carrier ... last on average about 20 years
- "US Navy Propulsion Systems". Federation of American Scientists. Archived from the original on 9 October 2006. Retrieved 2006-10-16.
power per reactor ... 140,000 shp
-  (correcting for the power output from 500 megawatts to 105.)