Chris Hi!
Letters on British ww2 bombs generally indicate the "filling station". I'll try and see whether I can find a list of the codes for these stations.
A Filling Station (or "Filling Factory") was a munitions factory which specialised in filling various munitions, such as bombs, shells, cartridges. Each of these stations had a "specialty" - for instance ROF Elstow filled "Blockbuster" bombs of 4000lbs, from 1942 onwards, then bombs of 2000lbs, 8000lbs and 12000lbs .
During WW2, the British Ministry of Munitions owned 12 permanent factories and 16 "wartime" factories.
The permanent one were:
Royal Arsenal, Woolwich.
National Filling Factory No. 1, Leeds, (Barnbow).
National Filling Factory No. 2, Liverpool, (Aintree).
National Filling Factory, Hereford.
Scottish Filling Factory (National Filling Factory No. 4), NFF Georgetown,Renfrewshire.
National Filling Factory No. 5, Quedgeley. See RAF Quedgeley.
National Filling Factory No. 6, Chilwell.
National Filling Factory No. 7, Hayes, Middlesex.
National Filling Factory No. 9, Banbury.
National Filling Factory No. 10, Whitmore Park, Coventry.
National Filling Factory No. 12, Cardonald.
National Filling Factory No. 13, White Lund, Morecambe.
The wartime ones were:
- ROF Aycliffe; ROF 59 (Filling Factory No. 8)
- ROF Brackla; Filling Factory No. 11;
- ROF Burghfield; Filling Factory No. 18.
- ROF Bridgend; Filling Factory No. 2.
- ROF Chorley; Filling Factory No. 1.
- ROF Elstow; Filling Factory No. 16.
- ROF Featherstone; Filling Factory No. 17.
- ROF Glascoed; Filling Factory No. 3.
- ROF Hereford; Filling Factory No. 4.
- ROF Kirkby; Filling Factory No. 7.
- ROF Queniborough; Filling Factory No. 10.
- ROF Risley; Filling Factory No. 6.
- ROF Ruddington; Filling Factory No 14.
- ROF Swynnerton; Filling Factory No. 5.
- ROF Thorpe Arch; Filling Factory No. 9
- ROF Walsall; Filling Factory No. 15