Since when he Francis Wallace Grenfell's rank in the British Army been the highest rank?
Francis Grenfell, 1st Baron Grenfell: Field Marshal Francis Wallace Grenfell, 1st Baron Grenfell, GCB, GCMG, PC (29 April 1841 – 27 January 1925) was a British Army officer. Field marshal (United Kingdom): Field Marshal has been the highest rank in the British Army since 1736.
i don't know