Here at NASWI and at all the other bases we've got DSN (Defense Switched Network) numbers and commercial numbers.
For the base here, the government appears to have bought out the 257 block of the 360 area code. Everything on base is 360-257-XXXX except a few oddballs here and there that were probably added afterward.
To dial another extension on base, you can just dial 7-XXXX. To make a DSN call, 8-XXXX. PSTN just dial 9 as usual.
In terms of the DSN...
The different continental commands are divided up using area codes, the US (CONUS) being 312... et cetera.
Each base is assigned a 3 digit exchange code, then the last four digits are, of course, the subscriber number.
All of the numbers at this base are 820-XXXX.
I believe the base here has a Nortel CS1000. The digital phones are all the Meridian 1 type with the "Program" key instead of the Feature key, and they have the two-tone high-low ringer. Most of the phone lines on base are just analog phones, however. The rest are cheap cordless phones (V-Tech, Panasonic), and then a lot of the single line phones are
Cortelco Centurion phones.
Here's a link to the DSN website that talks all about it:
https://www.disa.mil/Services/Network-Services/Voice/SBU-Voice/Using-DSN
