The is one of the few of OH's unnamed photos which we have managed to identify since we started his tree:
He's Robert Henry Alexander Cotton, 1893-1960, OH's first cousin twice removed (in later years he was the spitting image of OH!). This photo was taken in June/July 1911 when he was first posted aboard HMS Renown.
EDIT: OH points out the photo wasn't unnamed - it said "Bob" on the back!! lol