Don't know.
Quick google search reveals that :
"In the 1800s, countries around Germany were growing much larger, forming empires; yet Germany was not a unified country until 1871. To counter the feeling of vulnerability and the stigma of youth, German nationalists in the mid-nineteenth century began to use the swastika, because it had ancient Aryan/Indian origins, to represent a long Germanic/Aryan history.
By the end of the nineteenth century, the swastika could be found on nationalist German volkisch periodicals and was the official emblem of the German Gymnasts' League.
In the beginning of the twentieth century, the swastika was a common symbol of German nationalism and could be found in a multitude of places such as the emblem for the Wandervogel, a German youth movement; on Joerg Lanz von Liebenfels' antisemitic periodical Ostara; on various Freikorps units; and as an emblem of the Thule Society.
On August 7, 1920, at the Salzburg Congress, this flag became the official emblem of the Nazi Party"
Shadow over Innmouth was written in 1931.