The USS Macon was one of the largest airships in the world. This photo is dated 1933, during her construction. That's an "duraluminum" hull. You can read about her career and death at Wikipedia.
If you find this photo fascinating, you really need to look at the large-size version. I can't believe those guys are on top of those ladders.
Found at x-ray delta one's Flickr photostream, via Sharp as Teeth and Stars.
Addendum: This re the men on the ladders (hat tip to Soubriquet):
As those ladders got higher and higher, they swayed more and more, and the workmen became afraid, refused to climb, and quit.
The project slowed almost to a standstill, until Nevil had a brainwave, just to the east of Howden, was the port of Hull, south, across the estuary was the port of Grimsby, and in both of those, there were a great many deep-water sailors, many who had served in the days of sail, and square-riggers. They were used to climbing aloft and working whilst moving, swinging, rolling, and they were eager for work. These men had no fear whatsoever of the heights, and the project was soon back on line.