Fire Control Mark 7 (Range Keeper)

YEAR: 1930
ITEM: Analog Computer
COMPANY: Ford Instrument Company, Inc.
COUNTRY: USA
IN OUR COLLECTION: Yes

This electro-mechanical computer was used on the USS St. Louis (CL-49) to provide firing solutions and control the big guns (6") on the St. Louis. The St. Louis (AKA the "Lucky Lou") was the first ship to make it out of Pearl Harbor on the morning of December 7, 1941.

The metal label attached to this item identifies the type of guns that were controlled by this computer, the time of flight cam gear, and the manufacturer. The Date, Inspector, Weight, and Serial number are not filled in. The Mark 7 version seems to be the first one that is designated as a Range Keeper rather than a computer. The label is somewhat difficult to read but you should make out the following:

This computer used both electric inputs and hand-operated inputs (mechanical). Radar information was fed directly into the computer by electric wiring. However, a large number of important inputs had to be set up by hand, generally by turning knobs or handles that would, in turn, move gears within the computer. For instance, the Mark 7 had seven knobs (Wind Speed, Ship Speed, Target Speed, Target Angle, Wind Angle, True Bearing, Deflection Correction), and turning each one would set the internal gears so that a firing solution could be computed. The settings could be monitored by the operator simply by looking at a series of dials on the computer display. (The operator stood and looked down through a glass top, beneath which were the current settings for the computer.) There were also handles that needed to be set.

The earliest Range Keepers (first deployed in 1916 during WWI) provided a firing solution, but the sailors had to aim the big guns to the correct settings provided by the computer. However, sailors often became fatigued in battle and didn't move the guns to the correct settings. This 1936 Range Keeper sent the firing solutions directly to the big guns (electrically, by controlling servo-motors that aimed the guns).

We have tentatively dated this computer to 1936 while we complete our research. The National Museum of the United States Navy in Washington, DC has informed us that they do not have any records that allow them to track the serial number of the computer. They pointed out that so many ships were being built in the mid and late 1930's that the Navy didn't have time to track individual parts of a ship. The "Lucky Lou" was launched in 1938 and its keel was laid in 1936. We have dated the computer to 1936 with the assumption that it was ordered as that ship was being built.

We hope that the images of this computer provide you with a new perspective on computing and an appreciation for the ingenuity of those men and women who developed this computer. We are used to seeing computer boards and wires in a computer...but to realize that the decision-making (firing solution) was done by gears is really quite amazing.

This is not the entire Range Keeper. Parts of it were too heavy to remove from the ship and were lost when the ship sank in heavy seas while it was being towed to a salvage dock in 1980. This section alone weighs over 200 pounds.

We have a Navy manual for the Mark 7 with inspection documents that show that this computer was being used as early as 1930. It's entirely possible that the Mark 7 was first manufactured in the late 1920s. The model we have (Model 16) in our collection was likely made in 1936.

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