Series Number Id: GSGS 2742; Sheet number: 51b NW; Edition number: 5a, Location: Research Collections; Fonds: WW1 Trench Maps: France; Box number: PC10; envelope_number: 270, Manuscript: artillery targets in Thelus - Farbus area (for Battle of Arras); other markings north of Arras & in La Targette area; From Major J. C. Thomson (20th Siege Battery).