I may have posted this already, but anyway here is a better scan, i think.

From ‘Principles Underlying Radio Communication’, US Army  Signal Corps, 1922, p338 339:

“Good signals have been received from European long-wave stations on submarines off the

New England coast when the top of the loop was submerged 8 feet below the surface. Signals

have been successfully transmitted from a submarine to a distance of 3 miles, with the top of

the loop submerged 9 feet below the surface, using a 1-kilowatt transmitting set.”

Keep in mind that is with a spark transmitter, not the most efficient means of generating RF

per kW expended. The submarine forms one leg of the loop antenna.

via: Hue Miller,  K7HUE