All very different from whatever was dropped at Keevil, there's a bit of info on the 1916 techniques here, if you scroll to the end of the text about Lt Murray:
https://skipperswar.wordpress.com/20...may-13th-1916/
Somewhat similar techniques were used in support of the Allied advance on the Western Front in the last weeks of WW1, when ammunition boxes and baskets of pigeons were dropped from Corps Recce aircraft.