What form must incoming personnel complete for the unit mail room?

The correct choice, DA Form 3955, is crucial for incoming personnel as it serves as the official form used to request a change of address for military personnel. This form is essential in the unit mail room because it helps to manage the accurate delivery of mail to service members by updating their mailing information in the system. Proper completion of DA Form 3955 ensures that all personnel receive correspondence and packages at the correct address, which is vital for maintaining effective communication and ensuring that important documents are not lost or misdelivered.

In comparison, the other forms listed do not serve the same purpose in the context of managing incoming personnel mail. DA Form 3940, for instance, relates to a different administrative function, while DA Form 3999 and DA Form 2935 are utilized for other forms of military management and reporting. Thus, DA Form 3955 is uniquely suited for the needs of the unit mail room in establishing accurate address records for new members.