Ship Gun Fire-control System - US Navy Systems - MK 37 Gun Fire Control System (GFCS) - Mark 37 Director

Mark 37 Director

The function of the Mark 37 Director, which resembles a turret with "ears" rather than guns, was to track the present position of the target in bearing, elevation, and range. To do this, it had optical sights (the rectangular windows or hatches on the front), an optical rangefinder (the tubes or ears sticking out each side), and later models, fire control radar antennas. The rectangular antenna is for the Mark 12 FC radar, and the parabolic antenna on the left ("orange peel") is for the Mk 22 FC radar. They were part of an upgrade to improve tracking of aircraft.

The Director Officer also had a slew sight used to quickly point the director towards a new target. Up to four Mark 37 Gun Fire Control Systems were installed on battleships. On a battleship, the director is protected by 1.5 inches of armor, and weighs 21 tons. The Mark 37 director aboard the USS Joseph P. Kennedy, Jr. is protected with one-half inch of armor plate and weighs 16 tons.

Stabilizing signals from the Stable Element kept the optical sight telescopes, rangefinder, and radar antenna free from the effects of deck tilt. The signal that kept the rangefinder's axis horizontal was called "crosslevel"; elevation stabilization was called simply "level". Although the stable element was below decks in Plot, next to the Mk.1/1A computer, its internal gimbals followed director motion in bearing and elevation so that it provided level and crosslevel data directly. To do so, accurately, when the fire control system was initially installed, a surveyor, working in several stages, transferred the position of the gun director into Plot so the stable element's own internal mechanism was properly aligned to the director.

Although the rangefinder had significant mass and inertia, the crosslevel servo normally was only lightly loaded, because the rangefinder's own inertia kept it essentially horizontal; the servo's task was usually simply to ensure that the rangefinder and sight telescopes remained horizontal.

Mk. 37 director train (bearing) and elevation drives were by D.C. motors fed from Amplidyne rotary power-amplifying generators. Although the train Amplidyne was rated at several kilowatts maximum output, its input signal came from a pair of 6L6 audio beam tetrode vacuum tubes (valves, in the U.K.).