According to the 1911 census 21 Endsleigh Street is occupied by female workers at the Duchess of Marlborough's Home. I see no reference to soldiers and I think it was probably being used as a home for "fallen women" at this time.
There's the Lady Superintendent, needlework matron, cook, kitchen maid, house maid, and two creche nurses. No residents are listed.
Only today I've discovered that on 16th May 1923 my mother's unmarried cousin gave birth at this address, although her home address is also given. No father's name, of course, although the second forename of Gordon might be a hint - or it might not! In the right hand margin of the birth certificate is a note "Adopted" but no more.
My mother gave a hint that this child existed, but it's taken me 10 years to find Richard Gordon Senior. The National Children's Home may have had something to do with his adoption. Richard might still be alive. His name was probably changed. He may have children. I'd love to find them, but I suspect I won't!