Just scanned the arrival of the Great War supplement 'Over the Top'. Half price at present from Warhammer Historical.
This supplement primarily covers trench warfare in WW1. Not the most attractive gaming option but Alex Buchel has developed a very playable game using the excellent GW rules. He starts with an historical overview before setting out a whole batch of new rules and what he calls 'grand manoevres'. These add in heavy artillery barrages and some special troop types together with fortifications for defenders and stratagems for attackers. These are built into the points options so you can opt for bigger fortifications at the cost of troops.
There are new missions that are set in the context of actual battleground operations throughout the war. Followed by new army lists for the major combatants. All of this is generously illustrated with good figures and great scenery.
The supplement only covers the Western Front. So I will have to give some thought to how this could be applied to the Salonika campaign. Doiran is an obvious scenario choice. I also use these rules for A Very British Civil War and parts of the supplement will be useful for that.