In 1915, an airship base comprising two airship sheds and a hangar was established near Tønder. The first Zeppelins landed here in spring 1915, and primarily flew reconnaissance missions over Great Britain. The base was subsequently expanded to include a double shed (243 m long and 73 m wide) and was operated by a staff of 500. In July 1918, the base was bombed by British aircraft and never became operational again.
A defence installation called Sicherungsstellung Nord was built in 1916, extending all the way across the region of Southern Jutland from the Wadden Sea in the west to the waters of the Little Belt in the east. It was intended to prevent a possible British landing near Esbjerg in neutral Denmark, followed by an invasion of Germany from the north. Sicherungsstellung Nord was an extremely robust fortification, comprising two lines of trenches including more than 800 concrete bunkers. It featured roads, concrete bridges, military rail tracks, and signal and radio stations. It remained manned until the end of the war, but never saw action.