the .mil domain has an "master" source, just like .com or <your tld here>
it has a list of authoritative servers, just like .com or <your tld here>
You are reading your response incorrectly. your dig query ask for the
default, which is an "A" record. .MIL has no "A" rr at the apex. The
authority for .MIL, according to a.root-servers.net, is g.root-servers.net.
the NSlist for mil is:
$ dig mil. ns
; <<>> DiG 8.3 <<>> mil. ns
;; res options: init recurs defnam dnsrch
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4
;; flags: qr rd ra; QUERY: 1, ANSWER: 11, AUTHORITY: 0, ADDITIONAL: 11
;; QUERY SECTION:
;; mil, type = NS, class = IN
;; ANSWER SECTION:
mil. 2D IN NS CON1.NIPR.mil.
mil. 2D IN NS CON2.NIPR.mil.
mil. 2D IN NS EUR1.NIPR.mil.
mil. 2D IN NS EUR2.NIPR.mil.
mil. 2D IN NS PAC1.NIPR.mil.
mil. 2D IN NS PAC2.NIPR.mil.
mil. 2D IN NS A.ROOT-SERVERS.NET.
mil. 2D IN NS H.ROOT-SERVERS.NET.
mil. 2D IN NS G.ROOT-SERVERS.NET.
mil. 2D IN NS B.ROOT-SERVERS.NET.
mil. 2D IN NS E.ROOT-SERVERS.NET.