There is a patent class, A47G 21/08, for "serving devices for one-handed persons". This can be used to find, in the Espacenet database, 17 British patents between 1908 (as far back as coverage goes) and 1922. The earliest of these were only applied for in 1915.
British patents at the time usually gave the inventor's profession, Hence we have GB107915, applied for in 1916, which is by Edward Geoffrey Fisher, a Canadian private. It is illustrated below.
GB136966 was by Herbert William Duck, a farmer, and was applied for in 1919, and is illustrated below.
The occupations vary widely -- cinema proprietors and a surgeon are among them, though they are mainly engineers or, oddly, commercial agents.
Fore the same 1912-22 period there were 12 American patents, half of which date from the USA's involvement in the war from 1917. One such was particularly elaborate. It was by Charles Young of Maine, his Holding device for one-armed persons, illustrated below.
For the same period there are also 11 French patents, all dating from 1915 onwards.
These patents are sad to look at and to think of, but do show how patents provide a source of information for a grim chapter of history.