Despite our failure of recovery, the significance of this event cannot be denied. We are not alone.”— Report on U.F.O. codenamed "Palandine"
A terminal entry in the Pentagon mentions that it crashed in Hagerstown, Maryland in 2062. It could not be recovered. It was most likely a recon craft from mothership Zeta, which had been in orbit for about 4 centuries by then. However, many speculated it to be a spy drone from China or another country.
The Palandine is only mentioned in Fallout 3.