Read Halsey's Journal
From Halopedia, the Halo wiki
Read Halsey's Journal is an achievement in Halo: The Master Chief Collection. It is awarded by finding the Data Pad 2 on ONI: Sword Base in Halo: Reach, located under a set of stairs on the second floor of Sword Base's atrium.
The achievement is a reference to "Dr. Halsey's personal journal".