Hi Phil
As, thankfully William survived the war it makes it harder to track his progress through it !.
My best guess is, as he was E company he was probably sent out as a battle casualty replacement for the early losses in 1916. He doesn't appear on the medal roll (the date the battalion landed in France 18/11/1915). The fact that he later served with the RDC would suggest that he was wounded and no longer fit to serve overseas. as Harribobs says, if you download his medal card it should give you the date he arrived in France.