- 1920-26 Khyber Railway Engineer survey and construction
Colonel Gordon Hearn was assigned to the work of surveying and recommending the best route through Khyber Pass. Previously all surveys recommended a metre gauge(MG) track. However the proposal to use broad gauge(BG) was adopted and construction restarted in 1920.
Historical books online
- Permanent Way Through the Khyber by Victor Bayley 1939, first published 1934. Link to a pdf download PAHAR Mountains of Central Asia Digital Dataset. Archive.org mirror version.
- Bayley, Victor (1939). Permanent Way Through the Khyber. London: Jarrold