Taking the Metro?
Walking time: 15-20 minutes
Take the Blue/Orange Line and exit at the Smithsonian (link). The station has two exits, so make sure to leave through “The National Mall” exit at 12th St & Jefferson Drive SW.
Walk west on Jefferson Dr SW towards the Washington Monument, then continue walking past the monument towards the World War II Memorial.
Once you reach the World War II Memorial, walk around on the left side towards the JFK Hockey Fields until you see the DC War Memorial tucked away amongst some trees on the left. (link)
If you walked to the Lincoln Memorial you went too far.