Navigation before GPS

[Naphtali]

I was uncertain whether this query belongs here or in WW II forum. I chose here.

Before Global Positioning Satellite systems, how was precise location determined? I understand that two devices are able to accomplish this: sextant; and theodolite.

What are these things? Rather than request explanation of how each works, I would appreciate links to instructions/explanations.

What are the basic differences between theodolite and sextant? I have been told that sextants are to be used at sea while theodolites are to be used on land. But this is not particularly helpful in the absence of how and why.

I understand that air navigation was accomplished, perhaps, differently, that identifying precise location was difficult-to-impossible (Amelia Earhart's aircraft being an example??). Why?

 

[Lone_Ranger]

If you go back to WWII, most aircraft navigated by a combination of pilotage, and dead reckoning. Pilotage being comparing what you see on the ground to the chart you have. Dead reckoning is just your basic time, speed, and distance calculations. Adjusted for estimated wind speed and direction.

Dead reckoning can be quite accurate, but you have to back it up with pilotage. The longer the distance, or time you go between checking your dead reckoning the greater the error can be between where you're supposed to be, and where you actually are.

For long distance, over water flights, there was nothing to check your dead reckoning with. So those old aircraft all had a blister window somewhere, where the navigator could use a sextant to do celestial navigation. A sextant is just a device that measures the height of a celestial object above the horizon. You sight two or more stars, and consult a chart that will help you plot your position on a chart. Of course, you need to be able to see the stars. If it's cloudy, you may have a problem.

Along came the ADF/NDB. Which was a non-directional beacon on the ground, and a direction finder, in the aircraft. Basically any radio tower sends out a signal that the DF gear will point to. You just have to have a DF capable of picking up the frequency of signal that is being sent out. The DF will not give you distance to your "target" only the direction to the "station" Though if you plot two different "stations" and know where they are located on a chart, you can plot your position.

Earhart's problem was an apparent lack of understanding of her Bendix direction-finding loop antenna, which at the time was very new technology. The long DF antenna, that both Earhart, and Noonan, knew how to use was left behind in an effort to save weight. (Or out of laziness) Some say they felt it was too much trouble to crank in and out.

So they are left with dead reckoning for long over water flights where there was no accurate wind data, trying to find a tiny island, that was positioned 5 miles from where it was shown on the charts.

 

[Jauntyone]

I was a navigator in the Navy from 1988 to 1992. GPS was first introduced about half way thru my tour. Before, we used a sextant to get sun-lines, moon-lines, and star fixes that were calculated using complex formulae and corrections from the Nautical Almanac. These celestial fixes were absolutely obligatory, and were taken regularly. The captain took a personal interest in how often they were taken and how accurate they were. When the sky was too cloudy, we used dead reckoning. There was also a system called Loran C that used radio towers to fix position, but on the high sea, radio towers were few and far between.
Our primary electronic navigation system was SatNav--Satellite Navigation. It was a great big ol' machine that used the doppler effect and electronic signals from satellites that passed overhead to fix our position. Between satellites it would use it's own dead reckoning estimates to give us our longitude and latitude. It was very tempramental, difficult to set or re-set, and it's dead reckoning was less accurate than our own, as it didn't account for set and drift.
Close to land, of course, we used a gyro compass and different lighthouses, bouys, and landmarks that were charted to fix our position. Get a bearing on three or more of these, and where the lines cross is where you are.
We were absolutely in awe of GPS when it arrived--it just made everything so, so, soooooo much easier! Just press a button and presto! You got your position, accurate to within a few feet, at any moment, whatever the weather, no waiting for satellites to pass, no calculations or corrections. Still, celestial navigation remained the official way to fix position for a long time--I think it took the old-timers a while to really trust GPS.
I heard a while back that the Navy had given up completely on old-fashioned navigation and relied now solely on GPS. A bit sad, but understandable. [huh]

 

[rumblefish]

A bit more here:
http://www.thefedoralounge.com/showthread.php?t=31726&highlight=celestial+navigation
and here:
http://www.thefedoralounge.com/showthread.php?t=28365&highlight=navigation

 

[davestlouis]

At a very local level, I still use printed street guide books. My younger coworkers who swear by GPS are amazed at my antiquated technology.

 

[Chas]

The 1930's also saw the advent of radio beaon-guided navigation, one system used by the RAF for the night bombing campaign; GEE, which stayed in use until the 1960's.

And before the sextant was the Astrolabe, which dates back two millenia - in effect an early form of computer.

 

[JimWagner]

I was on air crew in the Navy in the late 60's. Our navigator, Wrong Way Smerzniak, attempted to use a periscope sextant, LORAN C, inertial navigation computer, Doppler radar unit and I think a red banded cane.

Most of the time the pilot ended up using dead reckoning while the radar operator put the radar on maximum range and compared coast line images to paper maps until we got close enough to land for VOR and TACAN to give reliable readouts.

We had fighter interceptors launched against us several times as we crossed the ADIZ (Air Defense Intercept Zone) at the wrong place approaching Iceland.

 

[Foofoogal]

I do not know much about it but sure can find a great out of the way BBQ place. Ran across one the other day almost afraid to go into as it was definitely not the best looking shack but sure was licking the plate on the way out. lol