Final answer:
Chapter 4 of Defense Travel Regulation (DTR) 4500.9-R Part 2 is referenced for in-checking of classified material.
Step-by-step explanation:
When in-checking classified material, the chapter referenced in the Defense Travel Regulation (DTR) 4500.9-R Part 2 is Chapter 4. This chapter specifically deals with the policies and procedures for in-checking classified material.
It provides guidance on the requirements for verifying, handling, and safeguarding classified materials. For instance, it outlines the responsibilities of the in-checker, the documentation required, and the steps to follow during the in-checking process.