Is there an idiom that military people use to encourage people before a mission. Something that means something like "Let's do this!" Is there any such idiom? It can be a sort of slang that's widely used too.
The Online Slang Dictionary says this word is:
slang used by Army soldiers to mean just about anything except "no." [It is] an enthusiastic yell or war cry ... meaning, hello, good, cool, or acceptance with enthusiasm
A blog post about the history of the word begins by saying:
"Hooah!" It is uttered at Army award ceremonies, bellowed from formations, and repeated before, during, and after training missions. You can hear it shouted by Air Force Security Forces, Pararescue, and Combat Controllers. The word HOO-YAH is thundered out by Navy SEALs, Navy Divers, and Navy EOD, and by United States Marines who pronounce their motivational cheer as "OohRah!" All are said to be slightly different versions of each other.