For my US readers/friends, ANZAC Day is much like our Memorial Day, or perhaps like Rememberance Day/Veteran's Day (though that date is also commemorated there).
The specific date is the day when the Australia-New Zealand Army Corps (hence, ANZAC) landed at Gallipoli in 1915. During the Great War, Winston Churchill proposed a plan to open the Black Sea to the British Navy, involving a quick landing and overland march to capture Istanbul and take Turkey out of the war as an ally of Germany. Things did not progress quite according to plan. By the time the Army Corps withdrew from the peninsula, over 8000 Australian, 2700 New Zealander, and 65000 Turkish soldiers died. As is often the case in protracted battles, soldiers of both sides grew to respect and appreciate the bravery of their opponents, which (perhaps ironically) leads to better relationships between their countries after the hostilities.
They shall grow not old,
As we that are left grow old,
Age shall not weary them,
Nor the years condemn.
At the going down of the sun,
And in the morning
We will remember them. Lest we Forget