GPS, Plan B: US Navy teaches celestial navigation as fallback for cyberattack

I don’t think you understand navigation.


I’m just shocked nobody makes buggy whips any more. Where will we be when the oil runs out? Whipless, that’s where.

I work for a large Danish shipping company. We continue to make celestial observations every day, as a means of staying proficient. It is not enough to know how to do the observations and calculations, it is necessary to be able to do them accurately and quickly. GPS is very reliable, but it could fail or be turned off. We always use as many methods of determining position and speed as are available, including visual bearings of lights or landmarks, radar ranges, depth soundings, and Celestial observations. And we normally also have at least three GPS units, with antennas in different places and running on different power sources.


To keep accurate time, you just need to know how to find the rate of error of a chronometer using observable phenomena, like sunrise or apparent noon. Once you know the rate of error, you just keep applying it to get the actual time. And the almanac data can be calculated. The tables exist for convenience. I frequently torment cadets by making them do those sorts of observations and calculations, as well as tying obscure knots.


Sadly, most of what I know of celestial navigation I learned from Patrick O’Brian (I’m sure you know your torture of cadets follows a long tradition). But I thought calculating the orbits of the planets was calculus far more involved than the spherical trigonometry (not arithmetic) needed to determine position.

This thread got awesome. I love hearing of you bluewater sailors, most of my current seafaring is with a kayak paddle in hand with the landmarks or lights of NYC in sight.

It seems like they are assuming everything except GPS will still work. Is there anyone that still practices calculating artillery trajectories by hand for anything larger than the smallest howitzer?

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Well, chances are good no one has rescinded the laws of physics or principia mathematica :smiley:

Targeting involves a setup resembling a drafting table and accessories in “the plotting room” for shore batteries.

And you need spotters

They’ll use computers like these below, I believe they were made for artillery too. I have no idea where my dad got this 1945 vintage set, he was an artillery sgt in the Italian occupation. I’m sure the real navigators here will be amused. I also have my grandfather’s sliderule squirrelled away, finding log tables & someone who knows how to use it would be tricky.

EDIT:Found an awesome page of these circular sliderules & calculators: Scroll down to the bottom for the Radiac Nuclear Yield Calculator Set

The math to become licensed as a senior officer can be a little daunting. Besides the navigation stuff, there is quite a bit about buoyancy, stress and bending, and things like free surface effect. You do need to be able to do those calculations with a pencil and calculator. Of course, usually there is software that does those calculations. But when the power goes out and you get a call in the middle of the night about flooded compartments, you should be able to do the calculations quickly. It is a much more math oriented career than I thought it would be when I became a cadet.

Bowditch redid the whole (printed, at that time) “database,” at it were, having found the tables unreliable and in fact a hazard for (ocean) navigators. An amazing guy, his bio Carry On, Mr. Bowditch is worth a read:,_Mr._Bowditch . (Hey mods, is there a way to suggest this book for bOING’s Amazon Affiliate program?)

Self-taught. A super geek. Progenitor of some interesting, even notable family members. A happy mutant, in his way, I sense.

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Admittedly I’m a little rusty, but as someone who has taken a celestial navigation course specifically for sailing, I have a pretty good understanding and I stand by my position: a decent app on a phone could measure the sun/stars’ position far more accurately than a sextant - which iirc is somewhere around 0.2 arcminutes. Such a device could be completely disconnected from any network, waterproofed and duplicated several times over and provide a level of accuracy that a human with a sextant could only dream of achieving.

Edit: Hell, even if you were to keep the sextant, a calculator would at least let you get away with avoiding the painful amount of math you need to calculate position. Ugh, just thinking about the calculation and having to pull out paper trig tables is enough to give me nightmares. I don’t even want to do it with pre-computed tables.

I think he does, but he doesn’t understand that after Armageddon the EMP will have taken out all the GPS satellites, the iPhones and the rest of the microelectronics, but the sextants and trig tables will still work.

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Although the photo looks like a coupe of RAF Pilot Officers rather than USN midshippment…

Also note that after GPS became ubiquitous the government shut down the LORAN broadcasting stations, which would not be vulnerable to the same type of attack as GPS (though they’d only be useful in US Coastal waters).

From my experience, that’s the majority. Self driving cars can’t come soon enough.

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I’m actually surprised that naval vessels don’t have someone doing a solar and or/Celestial sighting every day just to confirm every other aspect of their voyage. It seems like a hackproof, relatively low cost thing to do on a daily basis. They certainly seem to have enough people running around on those ships.
Well if you can measure the angle between polaris and the horizon you got longitude.
If you can measure time difference between apparent noon and greenwich noon you have latitude. Repeat over several days you have a rough velocity vector. Not perfect but you’ll know if its america or india hopefully.

Determining latitude with a sextant is pretty easy. It’s longitude that’s the problem. You need some kind of accurate method to figure out time differences. I know! We should have the Navy sponsor a contest for someone to build an instrument that can measure longitude! They can give out a prize.


LORAN-C (not sure about A and B) was usable not only in the US but also Europe and the pacific rim, stations were deployed all over the US sphere of influence.