(military slang, now historical) Finished, dead, no more, gone; non-existent.
What shall I do? / My poor old dug-out is napoo.
(military slang, now historical) Dead.
verb
(UK, military, slang) To finish; to put an end to; to kill.
He will napoo the rations.
1984, John Masters, Man of War, 1984, US title High Command, page 230,
“No,” Merton said shortly. “We sit tight, they find us. If we both go wandering about looking for each other in the middle of the night, we′ll start a battle and the whole plan for tomorrow will be napooed.”