If there are two commanders-in-chief, there are two fleets; and these two fleets may act in conjunction, in opposition, or without reference to each other.
The fact of a machine being operated by one man does not, however, prevent the machine from comprising several machines, operated by several men.

A vessel of war, for instance, is operated as a unit by one man; the words "vessel of war," meaning not only the inert hull, but all the parts of personnel and material that make a vessel of war.

The captain does not handle each individual machine or man; but he operates the mechanism and the personnel, by means of which all the machines and men are made to perform their tasks.
Now the naval machine is composed of many machines, but the machines that have to be "operated" in war, using the word "operated" in the usual military sense, are only the active fleet, the bureaus and offices and the bases; including in the bases any navy-yards within them.

Using the word "operated" still more technically, the only thing to be operated in war is the fleet: but the head of the Navy Department must also so direct the logistical efforts of the bureaus and offices and bases, that the fleet shall be given the material in fuel, supplies, and ammunition with which to conduct those operations.

Like the chief engineer of a ship, he must both operate and maintain the machine.
The fleet itself is a complex machine, even in time of peace.