Help with WWII datum conversion

[louxwe]

I am working on locating some WWII Pacific wrecks and have a question. Does anyone know what Datum was used on Pacific area Navy Nautical maps during WWII?

thanks

 

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[Mackaydon]

What area of the Pacific are you looking in? What datum, specifically, are you seeking? Current speed? Depths? Magnetic Deviation? etc.?
No doubt the Library of Congress, Map Department has all the answers if the pros here are unable to assist.
Don....

 

[ScubaDude]

They're likely NAD 27 instead of the current NAD83 & WGS84. There should be free converters on line, just about any good GPS can do it. I'm only assuming that might be what your refering to

 

[wreckdiver1715]

Back during WWII, they did not use GPS and no datums were in existence. That date was strictly off plotting charts. However, today the military and the Coast Guard use the WGS84 map datum.

Tom

 

[ScubaDude]

I'm familiar with GPS history and usage, and didn't remotely mean to infer that it was around back then.

Map datums were and have been around for a long time. A datum is a simple set of ground rules that define what's where, and what is measured from what what.

A set of coordinates derived fifty years ago entered into today's modern GPS is not going to take you to that exact spot without converting one datum to another, you'll be very close as in 10's of meters but off nonetheless.

Try Google.

 

[wreckdiver1715]

My apologies ScubaDude, you are absolutely correct concerning the long time use of Map Datums.


Tom

 

[Dinkydick]

May I interject my findings.

I have a book which does not mention the word datum anywhere.
However it does mention "Reference Planes" and for the Atlantic Coast,
Argentina, Sweden and Norway the "Reference Plane" is "Mean Low Water".

Oh any by the way the book is called "H.O.No.9 American Practical
Navigator" by Bowditch the year 1943. I have the hard cover edition
and the price was $3.75.

This book also mentions Reference Planes of Mean lower low water, Mean
low water springs, Lowest low water springs, Low water Indian spring, and
and Lowest low water for areas covering the Pacific Coast, Great Britain,
Germany, Denmark, Italy, Brazil, Chile, Portugal India, Japan, France, Spain,
and Greece.

Hope this helps as it is the only Bowditch I have.

Dinkydick

 

[stevemc]

Datums have been used for many years. If you use a chart of the Bahamas, a regular modern chart, it says datum from 1850 geo survey. But of course there has been updating to adjust the positions for magnetic drift as all datums do. They were using datum adjustments way before 1850, as some charts in other areas will show. The modern datums on most topo maps list the datum, and they update, kind of like you wouldnt use an old marine chart or a topo map and use the compass rose without calculating the correct datum as the position would have moved. You could hike with the old charts, and you could navigate, but precise GPS would be out of the question using the old maps. You must calulate the magnetic drift, which moves annually.