I’m referring to the large (3-30 ft) vertical glass or acrylic sheets with a tactical map on the back, and the current sitrep marked on the front in grease pencil (typically in a rear HQ setting)
They were once common in war room scenes on TV and film (often sidelit, so the greasepaint glowed) unti lthey were supplanted by “more modern” computer displays, but they weren’t just a Hollywood invention: I saw them in actual use in the late 1970s and this question was inspired by a documentary clip from the 1960s. The benefits of eraseable grease pen or marker on a glass or plastic surface are obvious, but it seems to me that using a preprinted paper map or traced outline map as an opaque backing would be more practical and actually have higher visibility (from the front, anyway) I never saw them used “movie style” with the glass sidelit in darkened room so the grease marks glowed. Maybe that’s reserved for the really dramatic situations or (far more likely) for showing off to VIPs.
When I saw them in use, I was too involved in the events of the moment to ask silly questions like “How do you get the map on there? Is it tape or paint? Surely we don’t have a stockroom of local and world maps at various scales–is there some “transparent map specialist, third class” who draws them up on demand? Why is it transparent? Etc.” Now I wish I had.
In one case, the room was crowded, and opaque tac maps might have gotten in the way (then again, they might have simply chosen a layout that made more sense for opaque maps, like putting the map directly on a wall). In other cases, I can’t think of any advantage.
I got to go on a cruise on a Navy aircraft carrier once, including tours of interesting places like the bridge, and the bridge had one of these transparent maps. The reason became obvious really quickly: there were guys who were extremely well practiced at writing backwards on the map, so they could constantly be updating information on it from behind, yet not be blocking the view of it.
Concur with ntucker: the underground WW2 [coast artillery] Plotting Room here at the Fort was changed in 1950 to an Anti-Aircraft Operations Room, and had large vertical plexi sheets installed, with the local map permanently painted on: the plotters stood behind the sheets, and wrote backwards in greasepencil on them as the plots came in; on the other side were telephone operators, transmitting the info to various batteries.
Got this info from a man who was one of the greasepencil-weilding plotters, circa 1953. (Needless to say, they were training to spot Soviet bombers).
MrAru the First [divorced…] had as his tac position on the USS Spadefish plotting on the acrylic. It also has the advantage of the people in front of the glass can write on it with their own greasepencils possibilities, and erase them without disturbing the correct current info the plotters have marked.
With the advent of computers, these old things have probably all vanished=(
The side-lighting would allow the markings to stand out in a darkened room, while the people (and things) behind the board were in shadow and not a distraction to those looking at the board from the front. Think of them as the manual version of a big-screen TV
Jeepers! I’m used to looking at star charts, which have east and west reversed, and this frequently causes trouble when I’m reading off of terrestrial maps—I always have to stop and think whether I’m looking up at the sky or down on Earth.
I feel sorry for people who get used to reading terrestrial maps backwards!
Huh. Makes perfect sense, but for some strange reason I would have imagined they’d reverse north and south instead, since I automatically imagine myself facing north and then looking straight up. Interesting.
