The Western Front was bookended by the North Sea and Switzerland, but what were the practicalities of those northern and southern most points? Was there a Naval presence preventing forces landing behind enemy lines in the north? Were there armed troops in Switzerland preventing forces from penetrating behind the lines in the south? I'm intrigued because the intensity of the fighting would seem to lend itself to forces attempting to envelop those seemingly finite points of the front, and there's very little literature that I've come across that explains how forces came to stop any efforts to bypass those end points.
The Northern extremity of the line was the Yser Front and it has enormous symbolic significance because it was the last strip of unoccupied Belgian territory. It was a little different from the typical Western Front network of deep trenches and dugouts because the ground was saturated with water. Canals, the Yser River, and deliberate inundations were an important part of the defence, and in many areas breastworks of sandbags stacked above ground had to substitute for digging in. (Photo)
Here is what the extreme north of the front looked like in 1917, with a very thick belt of wire right out onto the beach.
In the South things were rather different as this is a heavily sloped and wooded area of marginal strategic significance. There was no continuous trench line here but rather a line of outposts; the southernmost French bunker was called Villa Agathe and is a minor tourist attraction today. (Photos)
Once Italy joined the war things got even more awkward because there was an area of Swiss territory that adjoined both Italy and Austria-Hungary, and it overlooked an important mountain pass where both sides' mountain troops fought bitterly. This photo shows Austrians digging a trench only a few metres from the Swiss side, from which it was taken. And here are Swiss and Austrian soldiers conversing across a border marker. At one point Italian artillery fire intended to fly over the Swiss area fell short and destroyed a large pre-war hotel the Swiss had built there.
The Swiss army was fully mobilized and pledged to defend the country against any invader who tried to move through Switzerland to outflank the other side.
Finally, as for North Sea amphibious operations. The Germans really were not in a position to do this as they were inferior at sea and any force they landed would have been in great danger of being cut off and forced to surrender. The British, even though they were superior, ultimately came to the same conclusion. Churchill wanted to seize the Frisian islands of Borkum and Sylt; Sir Arthur Wilson wanted to be bolder and attack the German outpost at Heligoland, just miles from their main naval base; and Jackie Fisher was boldest of all with his scheme to crash into the Baltic Sea, land an army in Pomerania, and march directly on Berlin. (!) All of these schemes were vetoed as too risky. British strength lay in dreadnought battleships, which fight with super-heavy artillery in the open seas. Bringing these ships in close to shore put them at an unacceptable risk of being ambushed by mines, submarines, or small fast-moving craft firing torpedoes. Ultimately, the Royal Navy's main contribution was to operate specialized bombardment ships, called monitors, off the Belgian coast in direct support of the troops.
