The Ru-20 Bodyguard is a unit of infantry soldiers in the Russian Army, and are referred to as "drones" due to their duties.
Instead of deploying sentry drones, the SGB uses Ru-20 "Bodyguard" Platoons for menial guard duties. Bodyguard units are not as well armed as their Spetsnaz counterparts, but do receive slightly more training than a typical Russian army soldier.
They are in the same formation as riflemen meaning there are 20 of them rather than 4 average drones you get with other command units. Along with that they can also utilize cover, meaning ever farther range, attack power, and defensive power than a combat drone. They are referred to as Guards Brigade when used by the King Spider, and Combat Drones when deployed by Bears to fortify uplinks. Despite being infantry, they cannot board BTR-112 Cockroach IFVs. Their main weakness, as with Force Recon infantry, is their lack of shielding, in which they are easy prey for anyone brave enough to fight. Despite their lack of a shield they are still deadly against most units except Riflemen and Artillery at range, taking around 20-25% of the health of most enemies before dying.
Unlike the other factions, the SGB does not use their drone unit as a form of static defense during Raid missions, instead replacing them with double-barreled unmanned turrets.
Behind the Scenes
It is unclear what "RU-20" stands for. For all purposes, these are conventionally-equipped human soldiers. The render above indicates they use AKMs, while wearing little body armor. Their helmets may or may not be modern Kevlar ballistic helmets, but certainly lag behind special-forces grade hardware. They do not seem to wear armored vests, although they could, like Spetsnaz, wear them under their field fatigues.
It is possible that Ru-20 stands for "Russian-20", in reference to their nationality and the size of the unit.