Η'-1 55, 56 Η':1933.0223:1 N 22305 Η':1933.0223:3 N 22306 Section Η' 5 Section Η' 6 Section Η' 7 Section Η' 8 ... 21 February 1933
East trench extension at start of work ... Scanned 2005 for the 75th anniversary exhibition and publication. 51 Horizontal (normal) ... 20 Feb 1933
East trench extension at start of work ... AMS 51 Horizontal (normal) ... 20 Feb 1933