U.S. NAVY BASIC MECHANISMS OF FIRE CONTROL COMPUTERS MECHANICAL COMPUTER INSTRUCTIONAL FILM 27794

So I've known about slide-rules for a while. What I didn't realize was that the mechanical principles of slide-rules were applied to fire-control computers on WW2-era Battleships. [link] These computers had slide-rule like cylinders that would rotate. As you aimed the gun sights "at" a target, the gun's coordinates were being mapped to a cylinder, which would move the gun a different direction (you have to aim the gun "higher" the further away the target is, to account for gravity "drooping" the bullet). In effect; the weirdly shaped cylinder inside the fire-control computer is a pre-computed solution that maps x/y coordinate inputs to a z-coordinate output (where "z" would be fed into the gun's raw aiming system). The different parameters of the gun were programmed in with gears and cranks, moving the cylinder around physically. For more details, see: [this video] Its a 20-minute video. The cylinder mechanism (of 2x inputs mapped to 1x output) is specifically talked about here: [this video] . Carefully crafted cylinders could be any pre-computed 2-input / 1-output function. --------- Mechanical computers are fun. Slide rules are but the simplest kind. People were using more complicated "mechanical computers" for very serious combat / rangefinding / etc. systems just a few decades ago, before the advent of modern digital computers.

From top of head I really enjoy: MAPMAKING PROCESS, THE [link] mechanism computer of fire control computer (a classic) [this video] Physical science documentary series whose exact title I can't recall. It has been a while. To find more, my method is to do the occasional PeriscopeFilm binge (on youtube that digitizes a lot of old media, with great descriptions), always find find something interesting I haven't watched. If style, delivery really good, there's usually something in description to point to more. Like "U.S. NAVY TRAINING FILM", which usually returns playlists, and videos in same era often share quality. The technical ones generally don't disappoint. Another one is The Best Film Archives with good military training playlists. Tangent for others: the one I wish to remember, is a deleted/banned channel, one of the original US archival footage channel, with I think 1000s of videos, that got wiped many years ago right when youtube started drm crackdown. It had a companion website with obsessive amount of detail and tags to find the perfect video. And from what I recall, it didn't feel like a business like periscopefilm, but a passion project. It was an incredible amount of work to have been wiped out.

A special–purpose computer is any device which computes an answer to a specific question given some input or initial conditions. An abacus or slide rule is not a computer because they are not designed for a specific question or problem (but they can of course be an aid to computation). With the Antikythera mechanism, the operator sets the machine to the current date, and then turns the crank to advance the date. The dials on the face would continuously show the positions of several planets, the phase of the moon, the eclipses, and possibly one or two other things. Charles Babbage’s Difference Engine computed the values of polynomials. The operator would set the coefficients of the polynomial, then turn the crank to compute successive values of that polynomial for successive values of X. He never finished it though. The firing computer on a WWII destroyer computed the correct elevation of the guns, based on inputs that encoded the position and velocity of the ship, the position and velocity of the target, and several other variables. [this video] General–purpose computers take as input a _program_, and the program specifies the problem to be solved. You could load a program for computing eclipses one minute, and the next minute load a program for computing polynomials or firing solutions, or load one to check your email. The hardware hasn’t changed, only the program and inputs have changed. Contrast that with the Difference Engine: to make the difference engine compute eclipses or