It is all at L'Enfant metro station..........according to the DC metro posters......

The National Air and Space Museum of the Smithsonian Institution holds the largest collection of historic aircraft and spacecraft in the world in 161,145 square feet of exhibition floor space. Wikipedia
Address: 600 Independence Ave SW, Washington, DC 20560
Opened: 1976
Hours: 
Open today · 10:00 AM – 5:30 PM
Function: Museum
Phone: (202) 633-2214
Public transit access: L'Enfant Plaza station
Architect: Gyo Obata