Fire-control System - Naval Fire Control

Naval Fire Control

The situation for naval fire control was more complex because of the need to control the firing of several guns at once. In naval engagements both the firing guns and target are moving, and the variables are compounded by the greater distances and times involved. Naval gun fire control potentially involves three levels of complexity. Local control originated with primitive gun installations aimed by the individual gun crews. Director control aims all guns on the ship at a single target. Coordinated gunfire from a formation of ships at a single target was a focus of battleship fleet operations. Corrections are made for surface wind velocity, firing ship roll and pitch, powder magazine temperature, drift of rifled projectiles, individual gun bore diameter adjusted for shot-to-shot enlargement, and rate of change of range with additional modifications to the firing solution based upon the observation of preceding shots.

Rudimentary naval fire control systems were first developed around the time of World War I.

For the UK, their first system was built before World War I. At the heart was an analogue computer designed by Commander (later Admiral Sir) Frederic Charles Dreyer that calculated rate of change of range. The Dreyer Table was to be improved and served into the interwar period at which point it was superseded in new and reconstructed ships by the Admiralty Fire Control Table.

The use of director-controlled firing, together with the fire control computer, moved the control of the gun laying from the individual turrets to a central position; although individual gun mounts and multi-gun turrets may retain a local control option for use when battle damage limits director information transfer (these would be simpler versions called "turret tables" in the RN). Guns could then be fired in planned salvos, with each gun giving a slightly different trajectory. Dispersion of shot caused by differences in individual guns, individual projectiles, powder ignition sequences, and transient distortion of ship structure was undesirably large at typical naval engagement ranges. Directors high on the superstructure had a better view of the enemy than a turret mounted sight, and the crew operating them were distant from the sound and shock of the guns. Gun directors were topmost, and the ends of their optical rangefinders protruded from their sides, giving them a distinctive appearance.

Unmeasured and uncontrollable ballistic factors, like high altitude temperature, humidity, barometric pressure, wind direction and velocity, required final adjustment through observation of fall of shot. Visual range measurement (of both target and shell splashes) was difficult prior to availability of Radar. The British favoured coincident rangefinders while the Germans favored the stereoscopic type. The former were less able to range on an indistinct target but easier on the operator over a long period of use, the latter the reverse.

In a typical World War II British ship the fire control system connected the individual gun turrets to the director tower (where the sighting instruments were) and the analogue computer in the heart of the ship. In the director tower, operators trained their telescopes on the target; one telescope measured elevation and the other bearing. Rangefinder telescopes on a separate mounting measured the distance to the target. These measurements were converted by the Fire Control Table into bearings and elevations for the guns to fire upon. In the turrets, the gunlayers adjusted the elevation of their guns to match an indicator which was the elevation transmitted from the Fire Control table — a turret layer did the same for bearing. When the guns were on target they were centrally fired.

Even with as much mechanization of the process, it still required a large human element; the Transmitting Station (the room that housed the Dreyer table) for HMS Hood's main guns housed 27 crew.

For U.S. Navy gun fire control systems, see ship gun fire-control systems.

Directors were largely unprotected from enemy fire. It was difficult to put much weight into armour so high up on the ship, and even if the armour did stop a shot, the impact alone would likely knock the instruments out of alignment. Sufficient armour to protect from smaller shells and fragments from hits to other parts of the ship was the limit.