U.S. Defense Mapping Agency Hydrographic Center, August 1970
Hi Everyone,
This cold-war era nautical chart from the U.S. Defense Mapping Agency centers on the Barents Sea, a marginal sea of the Arctic Ocean on the northern coasts of Russia and Norway. Note the use of the Mercator projection; its distortion allows ships to set their course along a straight line.
The compass roses on the map have two concentric circles; the outer one indicates true north, while the inner one shows magnetic north, which ships would use for navigation with a magnetic compass. Ships could also use LORAN or long-range navigation to determine their location using signals pulsed from radio stations. LORAN was developed by the U.S. during World War II but has since been replaced by GPS. The green and purple lines on the chart reference LORAN rates.
The small black numbers in the ocean are called soundings and indicate mean water depth at low tide. They’re sometimes measured in feet, but on this chart, they’re measured in fathoms– one fathom is equivalent to six feet. The contour lines in the ocean indicate areas that are all below or above a certain depth– the 100-fathom contour line, for example, is drawn around an area with a depth below 100 fathoms (600 feet). The blue areas on the coastline indicate shallow-water areas.
Besides information on water depth, the map includes hazards, console stations, and areas where fishing and anchoring are prohibited. The sets of purple squiggle-dashed lines near the coast indicate areas with a variable current. Now that we can (more or less) understand the notation on the map, what might this map have been used for during this period? Why would navigation in this area be important to the U.S.?
