Map Overlap: Warsaw Pact vs. NATO Grids

The Charles Close Society hasn’t updated its topical list of articles on military mapping since I wrote about it in 2015, but there is a new article by John L. Cruickshank (“More on the UTM Grid system”) in Sheetlines 102 (April 2015) that is now freely available on the society’s website. The connection to Soviet mapping is that Cruickshank discusses how both NATO and the Warsaw Pact produced guides and maps to help their soldiers convert between their competing grid systems. Unlike latitude and longitude, a grid system assumes a flat surface.That’s good for simplifying calculations of distance and area, but means you have the problems of distortion that come with any map projection.

Both the Soviets and Americans based their standard grids on transverse Mercator projections that divided the globe up into narrow (6° wide) north-south strips, each with own projection. These were narrow enough not to be too badly distorted at the edges but still wide enough that artillery would rarely have to shoot from a grid location in one strip at a target in another (which required extra calculations to compensate for the difference in projections). The American system was called the Universal Transverse Mercator (or UTM; the grid itself was the Military Grid Reference System, or MGRS). The Soviet one was known, in the West at least, as the Gauß-Krüger grid.

In his article, Cruickshank reports that by 1961 East German intelligence was printing 1:200,000 military topographic maps that had both UTM and Soviet Gauß-Krüger grids. By 1985 a full series existed that ran all the way west to the English Channel. Rather than print a full map series with both grids, the US Army produced intelligence guides to the conversion between them. Field Manual 34-85, Conversion of Warsaw Pact Grids to UTM Grids was issued in September 1981. A supplement, G-K Conversion (Middle East) was released in February 1983. As Cruickshank observes, both manuals have fascinating illustrated covers. Conversion of Warsaw Pact Grids features a map with a rolled up map labelled “Intelligence” standing on a grid and looking at a globe focused on Europe. G-K Conversion, on the other hand, shows an Eagle literally stealing the map out of the hand of a Bear using calipers to measure distances from Turkey to Iran across the Caspian Sea.

The article ends with the observation that the history of modern geodesy, which underpins calculations like the UTM and Gauß-Krüger grids, remains “overdue for description.” Since it was published a new book has appeared that goes a long way towards covering some of those developments (at least for non-specialists, if not experts like Cruickshank). In fact, map grids are one of the main topics of After the Map: Cartography, Navigation and the Transformation of Territory in the Twentieth Century by William Rankin (University of Chicago Press, 2016). The book is chock-full of fascinating discussions of new mapping and navigation systems that developed between the end of the nineteenth century and the appearance of GPS. Its focus is on three overlapping case studies: large-scale global maps like the International Map of the World and World Aeronautical Charts (which have their own connection to Soviet mapping), grid systems like UTM, and radionavigation networks like Gee and Loran. (The third of these was already the topic of an article by Rankin that I wrote about here.)

In the chapters on map grids, After the Map shows just how long even an ostensibly universal design like UTM remained fragmented and regional. The use of grids had begun on the Western Front during the First World War. It spread to domestic surveying in the interwar period and been adopted by all the major powers during the Second World War. But universal adoption of the principles involved did not mean adoption of a common system. Even close allies like the United States and Britain ended up just dividing the world and jointly adopting one or the other nation’s approach in each region: British grids were applied to particular war zones and a more general American system used for the rest of the world. Neither used a transverse Mercator projection.

Even once America and its NATO allies settled on UTM as a postwar standard – a decision made despite opposition from the US Navy and Air Force, who fought vigorously for a graticule rather than a grid – UTM maps did not use a single consistent projection but adopted whichever reference ellipsoid was already in use for a region. While those differences were eventually resolved, even the 1990 edition of Defense Mapping Agency Technical Manual 8358.1, Datums, Ellipsoids, Grids, and Grid Reference Systems, still included specifications for twenty British grids including the British and Irish domestic surveys (plus a further nineteen further secondary grids), as well as the Russian Gauß-Krüger. East German tank commanders should have been grateful that they could get away with only two from the Intra-German Border to the Channel!

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