Old documents: part 4

The final set of documents for Akim is located in X-16, but along with them, he also wants you to obtain a PDA from a sniper that's recently been spotted in Darkscape.
== Walkthrough ==
=== Document and PDA ===
The sniper can be found on the top of one of the [ collapsed tunnels] in Darkscape. However, as you arrive there, you discover that the sniper has been killed by a group of mercenaries that is still there. Beware of the APC on a road, and three turrets on top of the tunnels. Kill them (beware of a merc with M60) and grab the PDA from sniper's body, which can be accessed by climbing a ladder on the side of the collapsed tunnel. 
The document can be found in a booth atop the lower exit of the elevator shaft in X-16.
Return both the document and PDA to Akim. He pays you and reveals that the documents contain the information on a prototype military exoskeleton called SKAT-15, and gives you the instruction manual for it.
=== Reward ===
 The instruction manual says that SKAT-15 can be located on one of the roofs in Yantar; however in order to get it, you have to do some work as you're not the only one looking for that exoskeleton, as Akim said.
At Yantar, you discover that the entire area has been trapped with four turrets. There are also four mines inside the building with the SKAT-15 stash, around the body of the military with Healing Beril. The mines cannot be picked up.
The roof with the stash can be reached using either a crouchjump from the door, or the Octopus artifact obtained in Collector's stash X-18. After picking up the exoskeleton, a team of mercenaries led by Gaiter will assault the factory, setting up 3 turrets and mining the area up.
The exact location of the turrets mercs set up after picking the stash up:
 The ambush is not too difficult to escape with an exosuit and bulletproofing artifacts, and you can enlist the loner camp to the east of the factory in your defense against the assault. Make sure you return to destroy all three turrets after cleaning out the mercenaries.
=== About SKAT-15 ===
This is the earliest unique exoskeleton in the game, and you can easily beat the entire game in it. Initially SKAT-15 doesn't offer much carrying weight compared to some exoskeletons, but it can be upgraded with additional modules. There are better armors in the game, but they will be available far down the story, and they usually don't provide the same survivability. Don't look at the bulletproofing percentage: it's the same for all exoskeletons, so you can use the un-upgraded version just fine. Refer to Armor for details.
The modules are obtained for different quests and are to be inserted in the specific order to upgrade the suit:
* The system that activates the modules - for Thermal insulation;
* Upgrade part 1 - for Doctor's locket;
* Upgrade part 2 - for Sakharov's medical bag.
This suit can auto-inject drugs (medkits, antizombine etc) and apply bandages when you bleed or your health is low. You can activate or deactivate the system with a hotkey bound in the settings. Your hands remain free, so you don't have to holster your weapon to heal yourself. Additionally, it uses less medicines than with the manual application.
SKAT-15 makes you essentially invulnerable to mosquito/plague zombies' attacks as long as you have bandages (max out your chemical burn resistance with artifacts, and you won't even notice the attack, the suit will only waste a couple bandages on it), and also lets you survive after a 7.62x51mm burst into the body if you have scientific medkits, as the suit is capable of restoring your health to 100% several times per second. See Sakharov's and Doctor's exchanges on where to find the scientific medkits in unlimited quantities, and Game Economy#Bulk artifact cooking on how to cook the artifacts to exchange.
== Notes ==
* The instruction manual isn't really needed for anything besides reading it yourself. You can give it to Informant for his "one-time cyclic" task.
* Following the classic game design practices of OP-2, the mines will inexplicably respawn as soon as you pick the stash up, forcing you to fight in a single spot. Not only that, but they respawn periodically. However, there's still plenty of ways you can escape out of this to fight without being glued to one place.
* The graffiti near the dead sniper (Так будет с каждым) can be translated to "So it will be with everyone like this" or "This is what happens to people like this" (the second translation is more likely), signed by KamikaZze, the lead developer of of OGSE (Link to his YouTube channel).
** This confirms that OP 2.2 uses the OGSE version of Darkscape, without the tunnel extensions (unlike in Narodnaya Solyanka 2016). 
*After the ambush at Yantar begins, Gaiter sends a message to his indignant mercenary squad not to use grenades to avoid damaging the armor.
**This apparently does not include underbarrel grenades, so be prepared for those.
== Bugs ==