[Crosseye76]

The Black paint job was standard due to the way the Subs were taught to operate in training and wargames during Peacetime.

During the day, the boat would remain submerged, listening for ships and conducting regular Periscope observations. They would surface only at night to charge batteries and move to new locations as needed.

Once war broke out, that very cautious method pretty much went out the window, and the Subs began staying on the surface longer day and night, and borrowed the U-boat doctrine of Night Surface attacks.

Black was still thought to be the best color..... Black sub against a dark background for Night attack. But experiments showed that a dark gray was the best in hiding the surfaced boat. So, along with other grey schemes, the Measure 322 / B or "Dark Grey" paint job came into being. I think it was Bill Ruhe in his book that remarked on how well it worked. He was not sure about it, but was won over after exercising against another Boat that had it recently applied.