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Subject
- Engineers.[remove]6
- Engineering.2
- Aeronautical engineers.1
- Aeronautics, Military.1
- Aeronautics.1
- African American engineers.1
- Airplanes--Design and construction.1
- Airships.1
- Akron (Airship)1
- Cascade Range.1
- Cascade Tunnel (Wash.)1
- Douglas Aircraft Company.1
- Douglas, Donald W. (Donald Wills), 1892-1981.1
- Helicopter pilots.1
- Helicopters.1
- Helium.1
- Hydraulic engineering.1
- Inventions.1
- Inventors.1
- Railroad tunnels--Washington (State)1