Fire Control Mark VI (Range Keeper)

YEAR: 1922
ITEM: Analog Computer
COMPANY: Ford Instrument Company Inc.
COUNTRY: USA
IN OUR COLLECTION: Yes

This unique computer is the oldest computer in our collection. An earlier version of this computer, the Mark I, was first tested on the USS Texas battleship in the summer of 1916. (Keep in mind that the US declared the "war to end all wars" on April 6, 1917.)The Navy was impressed with the performance of the Mark I and by 1917 the computer (also known as a Range Keeper) had been installed on at least four battleships... the USS New York, USS Wyoming, USS North Dakota and the USS Pennsylvania.

This computer was used to aim the guns on US Navy ships. It could calculate, in real time, an astounding number of variables for its time. It did not use any electricity!! All calculations were done by gears and the outputs were shown on the display.

The metal label attached to this item makes clear that, as far as the Navy was concerned, it was a computer. Later versions of this computer were commonly referred to as Range Keepers. The label is somewhat difficult to read but you should make out the following:

U.S. NAVY BUREAU OF ORDNANCE
COMPUTER
MARK VI MOD.7 SER. NO. 656
INSPR. (US Anchor stamp) DATE ___ WT 103 LBS
5" - 38 CAL 2500 F.S.I.V.
O.P. 551 ORD SK 61190
manufactured by
INTERNATIONAL BUSINESS MACH CORP
Endicott, New York
LICENSED BY FORD INSTRUMENT CO INC.

This mechanical computer was made completely of gears. This computer determined how the big guns on the ship were to be aimed at the enemy ships. It was designed to be bolted to the deck of a Navy ship and actually had a sight vane built into the computer to determine the enemy target's relative angle. All data was entered by a sailor or sailors standing around it.

This computer used only hand operated inputs (mechanical). All the data used for computing the firing position for the big guns had to be set up by hand, generally by turning knobs or handles that would, in turn, move gears within the computer. The Mark VI 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.

We have tentatively dated this analog computer to 1922 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.

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 Range Keeper seems to be the most complete example in existence. It even includes the stand that was bolted to the deck of the ship and held the computing unit high enough for sailors to enter data. The model in our collection is missing the sight vane that allowed the sailors to manually locate the enemy vessel.

Related Items

      Related Item 1: Range Keeper Mk. 7

      Related Item 2: Time of Flight Clock

      Related Item 3: Fire Control Equipment: Range Keeper Mark VII