Searching for the keyword Stornoway on the military databases on Ancestry has yielded 445 names, and checking name #2 immediately presented a puzzle.
Robert Bruce, 9th Highland Light Infantry 330122, was killed in action on 20 May 1917 at the age of 22. His place of birth is quoted as Stornoway, Caithness. That is already an oddity, as Stornoway used to be in Ross-shire. Looking at the census returns from 1901, I find a Robert Simon Bruce, aged 6, who lives at 34 Bayhead Street, Stornoway, living with his parents John and Jessie (aged 60 and 50 respectively) and several siblings.
However, the military records do not show any confirmed connection with Stornoway. The service returns, showing warrant officers, non-commissioned officers and men, only say that this man came from Scotland.
So, although the evidence is strong, it is not strong enough for Robert Bruce, 330122 HLI, to be included in the listings for the Isle of Lewis.