Apex domains cannot have CNAME records.
Question and response
Question
dig CSD.DISA.MIL. NS
Answer
CSD.DISA.MIL. 4 NS dns1.DISA.MIL.
CSD.DISA.MIL. 4 NS dns5.DISA.MIL.
CSD.DISA.MIL. 4 NS dns2.DISA.MIL.
CSD.DISA.MIL. 4 NS dns3.DISA.MIL.
CSD.DISA.MIL. 4 NS dns4.DISA.MIL.
Authority
The response has no authority records.
Additional
DNS1.DISA.MIL. 3 A 152.229.110.232
DNS2.DISA.MIL. 3 A 131.77.60.232
DNS3.DISA.MIL. 3 A 214.3.125.232
DNS4.DISA.MIL. 3 A 214.23.245.6
DNS5.DISA.MIL. 3 A 215.65.126.185
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0