With regards the "helicopter" sound it is actually the sound of a mounted machine gun.
For the whole shooting of the show out in the open, the crew didn't actually shoot in Turkey itself. They actually stayed at home, in Melbourne. The crew managed to find a secluded hill range and a local gun range to film on, and even built trenches there. While they did go to Gallipoli, the scenery was altered too much to actually create the impression of the landscape.
In ep 3, the soldiers are talking about the Turks, that they live in a country called Turkey. Turkey didn't exist during WW I, it was the Ottoman Empire back then. Turkey as a country, was founded after the wars, october 29th 1923, by Mustafa Kemal Atatürk.
Most of those who smoke throughout the series, smoke filtered cigarettes. Filtered cigarettes weren't introduced until the 1950's.
Soldiers in the Australian or British armies never refer to superiors by rank e.g. General Birdwood - "Sir" is the only appropriate thing to say.