One of the more interesting personal projects I worked in over the past two or three years related to the location of aerial signs built in Ireland during the second world war. You can see the output of that project on the Eiremarkings.org website and I am planning to put a research paper together on the subject as well.
The signs were built in 1942-1943 along the coast of Ireland to market the territory as not Northern Ireland or the UK, or any other place an aviator might have wound up lost. They were built at the instigation of the United States ambassador in Ireland at the time to reduce the risk of American pilots landing in Ireland and being detained by the Irish authorities. Locally, people were informed that they were built as neutrality markers to prevent accidental bombings. The fact that a number of such bombings had happened supported that rationale. Most of the signs were built close to the locations of coastal watch points, and after they were built, they were also numbered with the number of the nearest coastal watch look out post, all of which were numbered from 1 to 83. Maps with the numbered locations of the signs were given to American pilots and this made the signs useful as navigational aids; with the numbers they could work out approximately where they were if they saw one of the signs.
About the best known of the signs (until recently) at least was the sign on Malin Head but signs survived up and down the western coast and a number of them have been renovated, notably Loop Head in Clare and a couple of the signs in Mayo. Signs which were on arable land tended not to survive, and at least one sign was dismantled so that the stones could be used to rebuild walls. All of the signs for which I could find aerial photography evidence are matched on the site above. Not all of the numbers have survived and for at least three coastal watch locations, two large signs were built. Both signs for the Aran Islands still exist, although in the case of Achill Island and Slieve League, only one still exists or, at least is still visible.
Linked to this, and linked to a previous interest in lighthouses, and linked to the discovery of another pre-radar air navigation system in the US, I’m now interested in any historical navigation aids. Obviously a lot of work has been done in the area of ancient cartography and some of the tools of the navigators during the age of exploration.
The aviation navigation system built in the United States in the 1920s was called the Transcontinental Airway System (per wiki) and consisted of huge arrows and beacons, marking a path east/west and vice versa across the United States. There is a comprehensively illustrated write up on them here and additionally, with a little patience, the remaining arrows can still be seen from the aerial map services of Google and Microsoft (amongst others). In one respect, you’d have to wonder how much the existence of this navigation method influenced the creation of the coastal markers in Ireland almost 20 years later.
The navigation aids that humanity has designed in the interim, the radar based methods, and the automatic landing systems are far in excess of anything anyone flying across the US in the 1920s could possibly have imagined. A key fascination about the old methods is how they addressed problem solving. If you read the Terry Pratchett books at all, the third book, Equal Rites, refers to a tree marking system used to enable people lost in snowfall to navigate their way around the forest when they could not actually see where they were owing to the snow fall and the darkness. I have no idea whether such a system was implemented anywhere (I would not be surprised to be honest). Ultimately, every step in technology brings with it new problems to be solved, either for all time, or in the interim. So one of the reasons I’m interested in these things is not just in terms of what they achieved for themselves, but the extent to which they demonstrate our capacity for solving problems we might never have expected to exist until a point where, suddenly, they did exist.