A primary method of casualty prevention and control is use of the split-plant mode of operation. The purpose of the split-plant design is to minimize battle damage that might result from a single hit.

Most naval ships that were built primarily as warships have at least two engineering plants. Larger combatant ships have four individual engineering plants. Split-plant operation means aligning support systems, engines, pumps, and other machinery so that two or more propulsion plans and/or electrical generating plants are available, each complete in itself. Each main engine installation has its own piping systems and other auxiliaries. Each propulsion plant operates its own propeller shaft. If one plant were to be put out of action by explosion, shellfire, or flooding, the other plant could continue to drive the ship ahead, though at somewhat reduced speed.

Split-plant operation is not absolute insurance against damage that might immobilize the entire engineering plant, but it does reduce the chances of such a casualty. It prevents transmission of damage from one plant to another or possible serious effect on the operation of the other plant or plants. It is the first step in the PREVENTION of major engineering casualties.

The fuel system is generally arranged so that fuel transfer pumps can take suction from any fuel tank in the ship and can pump to any other fuel tank. Fuel service pumps supply fuel from the service tanks to the main engines. In split-plant operations, the forward fuel service pumps of a ship are lined up with the forward service tanks, and the after service pumps are lined up with the after service tanks. The cross-connect valves in the fuel transfer line must be closed except when fuel is being transferred.

Diesel propulsion plants are designed for split-plant operation only; however, some of the auxiliary and main systems may be run cross-connected or split. Among these auxiliaries are the starting-air systems, cooling-water systems, firemain systems, and, in some plants, the fuel and lube oil systems.

In diesel-electric installations, the diesel elements are split, but the generator elements can be run split or cross-connected. The advantages of this type of installation will depend on operating procedures as well as design.