If I am correct 2-59+ means the tank was put into service in February 1959 and certified for 10% overpressure.
Anyhow, 1959 was after WWII.
The swastika (as a character 卐 or 卍) is a geometrical figure and an ancient religious icon in the cultures of Eurasia, used as a symbol of divinity and spirituality in Indian religions. In the Western world, it was a symbol of auspiciousness and good luck until the 1930s, when it became a feature of Nazi symbolism as an emblem of Aryan identity and, as a result, it was stigmatized by its association with ideas of racism and antisemitism. Wiki
As you may know, numerous businesses used the swastika as a symbol before the Nazi's co-opted the symbol.
Here is an example:
Attachment 56593
I don't think the story of Nazi cylinders has legs when you consider that after WWII ended we were junking equipment in place rather than bringing it home. In view of that the mother lode of Nazi gas cylinders probably wouldn't have made the boat.