My father in-law was a photographer on the Russian front, he never used a light meter. I found this out after he visited us in Australia in the late eighties. He was shooting slide film on an ancient Agfa camera from the sixties, he wasn't using a light meter. Once or twice he asked me what I was shooting (the same film) at. Turned out he was invariably using the same shutter/aperture combination.
I developed his films after our Australian holiday and before he returned back home to Germany, very good to brilliant exposures, all without a light meter.
Cameras were sent up in unmanned Zeppelin ships to about 150-200 metres in height on a cable, fired off with cable, air or some other method, I'm not too sure really, then quickly pulled back down before they were shot down, this was on the Russian front. Another method of taking pictures was in trenches using a TLR upside down on a stick and a cable release. Composition was obtained by looking on the inverted ground glass.
Essentially if you shoot enough film for long enough and often enough and develop and print it yourself, you end up knowing what settings are required. I would guess that many war photographers may have started with a light meter, but probably didn't wear them out once they had their eye in.
Some press photographers I know never used a light meter and even when automatic cameras came along, still didn't use the inbuilt meter.
I can pretty much guess the correct (for me) shutter/aperture combination before I take a reading, invariably I'm within a bulls roar of agreeing with my light meter.
Sunny sixteen was what we used when I first started in photography, still works today.