Unsung heroes, animals played vital and varied roles in WWI

Machine gunners with mules cross a trench in France during WWI. (AP Photo, File)
In this undated WWI file photo, soldiers move toward the front with their machine guns and ammunition pulled by dogs in Belgium. (AP Photo, File)

PARIS — They were messengers, spies and sentinels. They led cavalry charges, carried supplies to the front, comforted wounded soldiers and died by the millions during World War I.