FOO - a Forward Observation Officer; a (now probably obselete) British Army acronym for the man dug in, right at the front line, observing where things friendly and not so friendly are located, and directing artillery fire, by telephone (or later, radio). Someone who keeps his head down below the parapet, as far and as often as possible.
Thanks to the anonymous webslave with a sense of humor at NOAA's SAA site for providing this image; sadly that site is now modernised, and foo-free, but the foo lives on here.