Global Warming, page-7

So it is for real. It was the 'seal hunters' that surprised me on the initial reading, I thought that practice was long gone, but no, apparently that is alive and well too (at least according to Wiki...).

Apparently SONAR was invented in about 1912, and it's feasible that enough was known about water density changes with salinity and temperature that a system with that capability would have evolved by 1922.

After seeing the claim it was published in 1922 by the Washington Post, I then thought how unusual it was for the Americans to use the metric 3100m instead of 10,000 feet or whatever it is exactly. But it seems that the scientific community had bought in to the Metric system very early on.