When I was in the Navy, the ship that I was on had a 48 inch diameter carbon arc searchlight on it. The searchlight worked by taking what was essentially two welding rods, pressing them together, and maintaining an electrical arc in order to create a searchlight beam that was bright enough to be seen for miles. In fact, by shining that light at a cloud, it was possible to send Morse code signals to other ships over the horizon.
When my ship was built in the mid 70’s, these lights weren’t made any longer, and the one that was on my ship had been salvaged from a WW2 era destroyer that had been decommissioned. Built in the days before electronics, the system that ran this searchlight was incredibly complicated. It was an analog power supply that ran on a system of motors and gears, with lenses focusing beams of light on various parts of the system that turned motors on and off, pushing the rods closer together, or pulling them apart, as needed to maintain the light beam. A technical manual for a 24 inch example can be found here.
By the time I reported aboard the ship, the light no longer worked and no one knew how to fix it. At one point as a young E-4, I took an interest in this searchlight and decided to get it working. I made a project out of it. I found a manual in the ship’s tech library, brought the control unit down, and spent several weeks rebuilding it. When we finally got the thing lit, it was amazingly bright. The light hadn’t worked in years, and I didn’t get so much as an “attaboy” for getting it working. Nowadays, it seems like you would get a Navy Achievement Medal for fixing that thing.
I tell you this as a setup and explanation of where I got this interest in how early electrical engineers solved problems that seem easy today using electronics. The focus today is on the Ford Mark I fire control system.
The Navy needed a way to calculate the elevation and deflection of Naval guns so as to put shells on target. This was no trivial exercise in math. Both the target and the gun platform were likely moving, the target might even be airborne, the platform might be rocking in heavy seas. Different shells were of different weights and ballistic coefficients. Or you might want to put a starburst shell 50 feet over the target for illumination. Ranges were sometimes 30 or more miles away. All of these factors required math in three axes in order to be overcome: direction, distance, and elevation. Enter the Ford fire control computer.
A frigate might have one. Destroyers had two, allowing multiple batteries to engage different targets. An Iowa class battleship had four of them. They were accurate enough that this computer was still in use until the battleships were retired in the mid 90s. 50 years old is not bad for an analog computer living in the age of transistors.
Check out this video on how the system worked to direct the secondary batteries on the 5 inch guns of the battleship New Jersey.
What can be done today with a laptop computer took an entire room of switches and a 3,000 pound box filled with motors, switches, relays, and gears. It was bulky, heavy, and more complicated than a box full of Swiss watches, but it worked. It worked quite well, in fact.
I consider myself lucky to have worked on that searchlight. It was one of the most interesting projects that I have ever taken on.