What were they trying to hide?

[Waterways]

This is Herculaneum Dock in 1907. There has been an attempt to doctor the photo. It is clear that one of the graving docks has been brushed out (not too well either). The graving dock was on the maps of the time and was there when I was a kid.

I wonder what was in the dock? A military ship of some sort? A foreign naval vessel? An early submarine?

Interesting.