Polis Kshatriya

The Polis Kshatriya are the closest thing Polis has to a military, since they are never directly involved in any conflict. The Kshatriya security branch is primarily made of Rangers, though it's possible that locals may join either as a full time soldier, or as militia.

Military
The Kshatriya is Polis's prime militia. They can be seen guarding their Station entrances and patrolling nearby tunnels. The vast majority of the security are made up of Rangers. Its leadership is unknown aside from Miller who is in charge of the Rangers and, by extension, Polis security.

Stalkers
The Kshatriya, like other groups, also acts as Stalkers. As seen in the Faction Pack, a Ranger may join a Stalker team. These groups scavenge Moscow for pre-war items such as computer parts, gun schematics, down to a basic poster. This is all in a attempt to preserve pre-war culture.

Polis, like many other factions, commission Stalker groups. In this case, it's the Kshatriya. Two named teams are known to exist - that led by Melnik, who ventured to the Great Library to find a fabled book, and the team led by Kuzmich, who also searched the Library, hunting for artifacts.

Metro 2033
Kshatriya Stalkers are not encountered in Metro 2033. However, their military arm, the Rangers, are seen many times throughout the game. They are only seen guarding Polis once however, during the level "Polis".

Metro: Last Light
Kshatriya's Military forces, the Rangers, are seen many times throughout Metro: Last Light. However, they are only seen guarding Polis once during the level of the same name.

Stalkers of Kshatriya are seen only in the Metro: Last Light DLC, Kshatriya level. This Kshatriya team consisted of five members - Kuzmich, the weapons expert and, most likely, leader, Shaman, in charge of cataloging all the artifacts, the Stalker twins, Su and Bar, along with their newest recruit, the Ranger Trainee. As Stalkers of Polis, they ventured up onto the surface, hunting for artifacts and information that might help preserve some of the lost culture of old Russia.

Their latest assignment was to explore the Great Library, one of the largest libraries in the world, filled with thousands of books and artifacts - a treasure trove for the team. Su, Bar, and the rookie Stalker were to explore the tunnels beneath the library, finding an entrance to it. Although they were looking for anything from the old world, Shaman asked the Stalkers to try and find the fabled "Map of Secret Metro" that would prove invaluable in mapping the Metro 2 lines.

Eventually, the Stalker found the Secret Metro 2 Map, avoiding all the hostile mutants and Librarians, and made it back alive, ending the Kshatriya's assignment.

Novel
Finally reaching Polis, Artyom seeked the Council of Polis for aid in defeating the Dark Ones to the north of VDNKh. He found them less that helpful, for they believed that VDNKh was not Polis' concern. However, Artyom persuaded them that if the Dark Ones breached the Metro, they would be their problem. Despite not believing this, the Council believed that Artyom was named as a chosen one at Polyanka, and would find a sacred book that would end the threat to the Metro. They told Artyom they would send help to VDNKh if he found the book. Artyom relented and prepared for the surface.

Together with Melnik, Ten, and Daniel, a Brahmin sent by the Council to aid him, Artyom reaches the Great Library to search for the book. However, the group are ambushed by Librarians and forced to split up. Inside the deepest rooms, Artyom searches for the book, but to no avail. While Daniel ties his shoe, Artyom goes on alone. Returning, he cannot find Daniel. Suddenly, he finds Daniel, impaled on a Librarian claw, slowly dying. The Librarian hides behind Daniel. Giving mercy to Daniel, Artyom shoots through him to kill the Librarian. Artyom searches Daniel's body, and finds some paper. With no time left, he makes it back to Melnik and an injured Ten. Melnik has to take Ten back to Polis, but Artyom cannot go empty handed back to the Council, with his advisor dead, so he is forced to take the surface route to Arbatskaya.

Trivia

 * It's never explicitly stated what the book Artyom was meant to find actually was, and whether it even existed. However, given the Council's belief in Polyanka as a "Station of Destiny", this book was likely made up.
 * It's likely that Kuzmich was a Stalker before he lost his leg, personally venturing out onto the surface. Now, it seems he directs the team from the relative comfort of their base.
 * Shaman is not actually a Kshatriya, but a Brahmin, a librarian of Polis, who likely accompanies the team to identify artifacts, catalog them, and ensure that they are kept safe.