The following are considered "The Essential War Collection" and are sold accordingly as a box set. Personally, I would disagree as to some of them being "essential":
1. Full Metal Jacket (Dir. Stanley Kubrick, 1987)
2. Where Eagles Dare (Dir. Brian G. Hutton, 1968)
3. The Dirty Dozen (Dir. Robert Aldrich, 1967)
4. We Were Soldiers (Dir. Randall Wallace, 2002)
5. Kelly's Heroes (Dir. Brian G. Hutton, 1970)
6. Memphis Belle (Dir. Michael Caton-Jones, 1990)
7. Battle Of The Bulge (Dir. Ken Annakin, 1965)
8. Escape To Victory (Dir. John Huston, 1981)
So, which would you replace and for what. You are only allowed to replace
THREE - don't try to cheat or I will
MOD you

I would take out:
2. Where Eagles Dare (Dir. Brian G. Hutton, 1968)
7. Battle Of The Bulge (Dir. Ken Annakin, 1965)
8. Escape To Victory (Dir. John Huston, 1981)
and replace them with
1. Battle of Britain
2. The Longest Day
3. Ice Cold in Alex