The Trials at Wool (at Bovington) in 1925 predated the establishment of the Experimental Mechanised Force by two years. From the photographs it appears they were particularly lookng at the performance of various vehicles - tracked, half tracked and wheeled - for moving the artillery. This included having them attempting to climb Gallows Hill, the occasion on which Adolphe Kegresse legendarily threw his hat in the air shouting "The wheel is dead" after one of his vehicles outperformed all the wheeled contenders. The letter or number contained in some of the captions designates the particular vehicle being tested, and these letters or numbers are displayed on the vehicles in the photographs.
The photographs in this post are captioned "general" - those with identified vehicles have posts of their own,
There are also photographs from test and exercises at Oakhampton in 1925, the Dominion Premiers Exhibition in 1926, and the Wool trials of February 1927.