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.