The raising of eight new Siege Batteries of the Royal Garrison Artillery was authorised by Army Council Instruction 145/1916, with effect from 13 January 1916.
| RGA Battery | Raised at |
|---|---|
| 99 Siege Battery | Forth Defences |
| 100 Siege Battery | Tynemouth |
| 101 Siege Battery | Sheerness |
| 102 Siege Battery | Portsmouth |
| 103 Siege Battery | Plymouth |
| 104 Siege Battery | Plymouth |
| 105 Siege Battery | Dover |
| 106 Siege Battery | Weymouth |
The ACI stated that numbers 103, 104 and 105 would have the establishment of a battery of 12-inch howitzers, and the others would be that of 6, 8 or 9.2-inch howitzers.