National Army Museum
The National Army Museum (NAM) in Chelsea has a library relating to general Army/regimental histories (requiring a reader's ticket). British Army musters, attestation papers, pension records and records of officer's services are not kept here but at The National Archives.
Presidency army officers
This India List thread is about a card index at the National Army Museum, prepared by Major V.C.P.Hodson (who published Hodson’s List of Officers of the Bengal Army). Unlike the published List, these cards hold the details of not just officers of the Bengal Army, but also those of the Bombay Army and Madras Army and include Civil Servants, Officers of Eastindiamen, Chaplains & other clergy. The list went on to include a good many people from the post East India Company period up to and including serving officers of the Second World War.
There are also some card indexes/papers prepared by Lt Col H K Percy Smith (1897-1975) who also prepared the Percy Smith card index collection at the Society of Genealogists
Note that there is no mention on the National Army Museum’s website regarding these index cards and they are not publicised.
FIBIS Resources
Strongly recommended is the article entitled “The India-related holdings of the National Army Museum” by Marion Harding and Jenny Spencer-Smith which appeared in FIBIS journal no 15. This is a most comprehensive account over nine pages long. FIBIS members can read this article online - see Fibis Journals. Non members may buy a copy of the relevant journal via the Fibis Shop.