Short answers, pulled from the story.
A forward observer directs artillery fire from a position near or behind enemy lines, adjusting rounds onto targets that gun crews cannot directly see. They are required to hold a secret security clearance because their situational awareness extends to the positions of allied units operating nearby. In the Army they hold the Military Occupational Specialty 13F and are officially called joint fire support specialists.
Enlisted Army forward observers attend an eleven-week advanced individual training course at Fort Sill, Oklahoma, covering call-for-fire techniques, field craft, and small unit tactics. Those assigned to airborne units such as the 82nd Airborne Division or the 75th Ranger Regiment must also complete the United States Army Airborne School. Ranger School is additionally open to both enlisted forward observers and officers.
A 13F is the Army enlisted Military Occupational Specialty for forward observers, also called joint fire support specialists. A joint fires observer, or JFO, is an additional certification available to observers and other select personnel from all military branches. JFOs are trained to control mortar, artillery, and naval gunfire support and to provide targeting information for close air support aircraft.
Naval artillery had a flat, high-velocity trajectory that infantry officers found difficult to predict and control during amphibious landings; rounds could not hit targets behind low hills and sometimes endangered friendly troops. Naval gunfire liaison officers were trained to translate ground-force objectives and fall-of-shot observations into commands that shipboard personnel could act on. The institutional framework for this role was formalized through Fleet Training Publication 167 in 1938 and a corresponding Army field manual in 1941.
The first certifying joint fires observer course was established at Nellis Air Force Base in 2004. It was moved to Fort Sill in 2006 and a second location was added at Einsiedlerhof, Germany, at the Warrior Preparation Center. The Marine Corps later established its own JFO course at Quantico, Virginia.
Mel Brooks, the actor, comedian, composer, and filmmaker, served as a forward observer, as did Maynard James Keenan, the lead singer of Tool. Country music singer Craig Morgan and actor Lombardo Boyar also held the role. Among Medal of Honor recipients, forward observers include Ronald E. Rosser, Brian Miles Thacker, and Ryan M. Pitts, alongside many others who received the award posthumously.