Is the soldier's weapon planted in the ground with his helmet (or shield in the case of earlier conflicts) on top of the weapon.

Seeing how this is a memorial specifically for World War I heroes, how fitting would it be for the memorial to use the helmet and weapon contemporary to that war as the symbol. Quite honestly, if I saw that memorial I would know instantly what it represented.

A cross in the middle of the desert? Perfectly meaningless symbol in a perfectly meaningless context.