Union Pacific 'Challenger' Project Reference |
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The Challenger Locomotives
William W. Kratville
William W. Kratville © 1980
Union Pacific Steam - Challenger Portraits
James L. Ehernberger
Challenger Press © 1993
Union Pacific Prototype Photos Volume #36 (4-6-6-4 Challenger)
Union Pacific Historical Society
ISBN#: 978-1-932704-28-0
Union Pacific Prototype Photos Volume #37 (4-6-6-4Challenger)
Union Pacific Historical Society
ISBN#: 978-1-932704-29-7
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