Why do modern militaries need desk-bound staff personnel?
In Classical and Medieval times, warfare was all about two armies charging into each other and individual soldiers engaging each other in melee combat with swords, clubs, or spears. The Persians invented highly mobile horse-mounted cavalry to supplant foot soldiers, while Indian warriors had chariot-borne archers. Later on, the English trained longbow archers while the Arabs had horse-mounted archers. Each cavalryman was supposed to procure his own horse, while each soldier procured his own weapons and arrows. Battlefield decisions were in many instances made before the fighting began, but they were more often than not, made in the heat of battle. For this reason, most generals had to be in the thick of combat. The conduct of wars was often purely tactical.
The invention of gunpowder-based firearms fundamentally altered warfare.
Firstly, gunpowder enabled the development of not only large bore longer-range cannons but also even longer-range rockets. This enabled an army to now have artillery. Also, since muskets and later on rifles could not only kill at range but also keep enemy troops pinned down at range, the army opposing them now needed more information than just where they are and how many of them there are. So, instead of scouts they now needed military spies. And they needed people to collate and analyze disparate intelligence reports. They needed an Intelligence Staff.
Secondly, weapons needed a constant supply of materials to keep them working. Guns require gunpowder, bullets, and cleaning oil to be constantly replenished. Since Armor Is Useless against bullets, soldiers now wore regular uniforms which in turn degraded more easily and needed replacing. Also, firearms-based combat increased the chance of losing sides in a battle and getting routed instead of being annihilated, so an army often had to pursue a retreating army over days, maybe even weeks or months. This meant a greater need for food, clothes, toiletries, and such. Supplies and procurement now needed a lot more centralized planning. Therefore, an army now needed a Logistics Staff. With automobiles and later on, engine-powered ships and aircraft being introduced into combat, the need for better-managed logistics increased even further.
Warfare itself now became more complex and multifaceted. Armies once only had Infantry and Cavalry, then they added Artillery, then Navies started playing an increasing role, and in World War One, Air Forces came into play. Artillery also became multifaceted with Fixed Artillery, Towed Artillery, Self-Propelled Artillery, and in more recent years, Anti-Air Artillery and nuclear artillery. Infantrymen now became specialized as Airborne, Helicopter borne, Amphibious naval infantry, Mechanized Infantry, Special Forces and regular grunts. Cavalry morphed into Armor and Aviation Cavalry, Air Forces further split into Fighters, Bombers, Transport aircraft for logistics, Recon aircraft, and Carrier-based Naval Aircraft, while the Navy now split into Surface ships, Submarines, Air assets, transportation ships and special forces formed from combat divers. A military therefore had multiple specialists, all of whom needed to be trained and coordinated in a larger-scale battle plan. Militaries therefore needed an Operations Staff.
Finally, as militaries became more complex, personnel needed managing at different hierarchical levels ie fire team, squad, platoon, company, battalion, regiment, division, corps, squadron, wing, fleet, etc. This necessitated multiple ranks at both enlisted and officer levels. Wherein previously, all officers were generals who came from nobility and they handled the advancement of enlisted men, nowadays an increased number of ranks meant a need for a Human Resource Management staff, known in the military as Adjutant Staff. With transfers to other units being the primary method of mitigating battle fatigue and at least in the US military, joint service operational staffs being a necessary assignment for senior officers looking to advance to flag rank, the need for career management specialists also known as Detailers increased.
Because the military now has to deal with equipment procurement, management of information, management of other people, more complex Rules Of Engagement as well as the usual gamut of problems that end up in a Court Martial, militaries now need dedicated legal staff ie military lawyers. And in today’s information-centric age, militaries also need Public Relations specialists to if nothing else counter bad propaganda whipped up by the enemy. Psy-Ops personnel in turn generate propaganda helpful to an army.
So, a Commander in the modern day will often have to be in a headquarters slightly in the rear with an entire command staff. This command staff will be comprised of adjutants, intelligence analysts, operation planners, and supply/logistics officers. A legal staff and public affairs staff sometimes but not always also deploys with the command staff.
This is why desk jockeys exist in modern-day militaries.
