21st Divisional Artillery Instruction 18 June 1916
Copy of G.H.Q. No O.B./21, dated 16.6.1916
In para 5. Section D Chap II, Training Manual R.F.C. Part II (page 46) it is laid down that a special prefix, followed by the sheet number and map square designation of the target, will be used as a call for artillery to open fire in case of emergency or when a specially favourable target presents itself.
By O.B./114 of July 1915, para 10, the special prefix ZZ was laid down for this purpose.
In O.B./1656 of 27.5.15, the signal ZZ was introduced as a signal from a contact patrol aeroplane that Infantry was held up by wire.
To avoid confusion, the special prefix to be used as a general call for immediate concentration of artillery fire on a certain point, as directed in para. 5, pages 46, 47 R.F.C. Training Manual, Part II, will be changed to LL.
This change will come into force from midnight June 18/19. all artillery and R.F.C. units must be warned of the change before that hour.
94th F.A. Bde.
For information and necessary action.
The call ZZ (Infantry held up by wire) for use to contact patrol aeroplane holds good.
18th June 1916. Brigade-Major 21st Divisional Artillery