Railroad Archives Online
- CollectionD0288 - Terence Wahl Collection
- Series004 - Northern Pacific Railroad Company
- Subseries Level 1014 - Photographs
- Subseries Level 2001 - Railroads--Equipment and Supplies
- Subseries Level 3002 - Diesel Locomotives
- ItemTRWahl0005 - Northern Pacific Diesel Locomotive 6511, Seattle, Washington, October 1951
- ItemTRWahl0006 - Northern Pacific Diesel Locomotive 409, Seattle, Washington, October 1951
- ItemTRWahl0169 - Northern Pacific Diesel Locomotive, Bellingham, Washington, undated
- ItemTRWahl0251 - Northern Pacific Diesel Locomotive 247, Bellingham, Washington, undated
- ItemTRWahl0262 - Northern Pacific Diesel Locomotive 215, Arlington, Washington, undated
- ItemTRWahl0263 - Northern Pacific Diesel Locomotive 217, Arlington, Washington, undated
- 23 more...