[Lou L]

I’m curious why the ships don’t stop for these operations (other than that would make them sitting ducks in wartime).

Underway replenishment was the US Navy's "secret weapon" for many years following WWII. Not so much as it was a secret, but the technology and the process required the utmost coordination and seamanship. There's a reasonable risk, but the payoff is high...fuel and supply up an entire Carrier Battle Group in an hour or two while on-station? Yes, logistics goes a long way in wartime.

[Thud]

Admiral Nimitz was the officer who developed and tested underway replenishment from oilers in the period between World Wars One and Two. It was regularly practiced by the Navy in the 1930s.

It was by no means a secret when World War Two started. The Japanese developed underway replenishment before the war. The Pearl Harbor striking force refueled its destroyers from oilers on the way to Pearl and again on the way back.

But the Japanese method could only replenish one ship at a time, trailing behind the oiler. The US Navy could replenish two ships simultaneously in 1939, one on each side of the oiler. Nimitz was responsible for that.