Silo network security codes

Silo network security codes is a keycard

Location
It can be found in Base Commander Martin Retslaf's desk in an office on the second floor of the Hopeville missile silo.

Behind the scenes
The transcript for this note is exactly the same as the transcript for the Fort Constantine launch codes appearing in Fallout 3, and as a result mentions Fort Constantine rather than the Hopeville Ballistic Defense Station.