1913 was, weatherwise, generally a rather dull and cool year in which both sunshine and rainfall were limited. Perfect, in fact, for the second of the large scale army manoeuvres carried out before 1914. The first, in 1912, had exposed Haig as dangerously incompetent. Haig commanded a crack Aldershot 'Red' force with an established command structure, against Grierson's rag-bag 'Blue' force made up of scratch units including Yeomanry and cyclists (classed as cavalry). Despite having all the advantages, including being the attacking side, Haig screwed up monumentally and Grierson walked all over him.
The 1913 manoeuvres again had a crack 'Brown' force under French of two Infantry corps and a cavalry division against a scratch 'White' force under Monro of Territorials and Yeomanry. This time there was no mistake and Brown duly won. White, however, did remarkably well - making excellent use of aircraft as spotters, motor transport and cyclists, by now correctly classed as mounted infantry. French had not done well, however. The problems in co-ordinating the movement of 50,000 men and 25,000 horses in the field had not been overcome and the generals were then practising very much a war of rapid movement. The stars were the aircraft, and they were to prove their worth in 1914 at the Aisne and the Marne.
Yet the following year it was French and Haig that led the BEF of 75,000 men in Belgium. Grierson died of a heart attack shortly after landing.
Between now and next year there will be a great deal of guff that portrays farmhands and factory workers flocking to the colours in August 1914 and 'in the trenches' a month later. This will all be bollocks and can be disregarded. The trenches didn't come until later, and the only men sent to France and Belgium were the BEF and slightly later those trained men in the reserve. That first phase of the war, very much a war of movement, was fought by the professionals and no doubt lessons had been learned at Brigade level and below from the 1912 / 1913 exercises that served them well.