cannon fodder

From cannon + fodder (food for livestock), i.e. food for enemy cannon fire.

cannon fodder (uncountable)

1. Military forces considered to be expendable.
   • 1930, Frank Richards, The Magnet, Victory for the Rebels

     "A foolish old half-pay officer," boomed Sir Hilton. "Go back to your club, sir, and play bridge with other superannuated cannon-fodder, sir."

2. (rare) Artillery ammunition.

• forlorn hope