General objectives of the stage: R&D is the third stage of Death Factory mission. Most important objectives in this stage are murdering two new scientists - Dr. Raymond Valentine and Dr. Edward Ashford. Due to the unique vertical design of the map and the presence of large number of personnel in the area, these objectives are not easy to achieve.
Exploration of the silo starts on its highest level and your task is to get to its lower levels, eliminating Dr. Valentine first (he walks between several levels) and then Dr. Ashford (he stays on the silo's lowest level).
Important information about the research department is that the main stairs even on lower levels are guarded by many factory guards. You have to react somehow to that fact. First solution is, of course, using the side stairs located in the conference room, close to the starting points. If you choose these stairs, you'll be able to avoid most of patrols.
The second, a much better option in my opinion, is obtaining researcher disguise (if you already have it, you can skip this step). Also in this case I recommend going to the conference room. Locate a radio, turn it on and wait until one of researchers comes to turn it off. Attack this person, preferably by stunning him and hiding his body in the closet.
When you reach the lowest floor, after eliminating Dr. Valentine (the walkthrough can be found in the next subchapter), you'll find factory guard disguise more helpful. In this case you can return to the top and get the disguise left there or attack one of single guards, for example the enemy at the previously mentioned side stairs (screen above).
Notice - I do not recommend exploring the lower part of the silo (where Dr. Ashford stays), until you murder Dr. Valentine, because otherwise you would have to unnecessarily return to upper levels.