AC ) ▁National ▁Bi ode f ense ▁Analysis ▁and ▁C ounter me asures ▁Center ▁( NB AC C ) ▁ ▁On ▁post ▁historic ▁sites ▁Fort ▁Det rick ▁has ▁three ▁sites ▁( and ▁four ▁structures ) ▁on ▁the ▁National ▁Register ▁of ▁Historic ▁Places : ▁ ▁The ▁N all in ▁Farm ▁House ▁( cir ca ▁ 1 8 3 5 ) ▁ ▁The ▁N all in ▁Farm ▁Spring house ▁and ▁Bank ▁Bar n ▁( pre - 1 7 9 8 ) ▁ ▁The ▁One ▁Mill ion ▁Liter ▁S phere , ▁the ▁" E ight ▁Ball " ▁( 1 9 4 7 – 4 8 ) ▁ ▁In ▁addition , ▁the ▁following ▁sites ▁on ▁the ▁installation ▁are ▁of ▁historic ▁interest : ▁▁ ▁A ▁rock y ▁kn oll ▁over looking ▁Frederick , ▁and ▁located ▁near ▁the ▁Old ▁Farm ▁Gate ▁( n orth west ▁gate ) ▁of ▁Fort ▁Det rick , ▁was ▁the ▁site ▁of ▁historic ▁structures . ▁The ▁Nov iti ate ▁Academy ▁of ▁Frederick ▁built ▁an ▁impress ive ▁estate , ▁Saint ▁Joseph ' s ▁Villa , ▁on ▁the ▁hill ▁in ▁ 1 8 9 5 . ▁This ▁was ▁located ▁there ▁because ▁of ▁Rest oration ▁Spring ▁just ▁to ▁the ▁north ▁at ▁the ▁base ▁of ▁the ▁hill . ▁The ▁Academy ▁moved ▁to ▁New ▁York ▁in ▁ 1 9 0 3 ▁and ▁the ▁Villa ▁was ▁subsequently ▁demol ished . ▁Dr . ▁Rud olph ▁R au , ▁a ▁Frederick ▁sur geon , ▁bought ▁the ▁land ▁in ▁ 1 9 1 1 ▁and ▁constructed ▁an ▁impos ing ▁white ▁m ansion ▁with ▁col