As in ww2 Philippines, or any other country so invaded and occupied... the list is endless over the millennia of human "civilisation"... Doubtful that I will "go to war" in the sense implied by the OP... but war may come to ME.. and if it should my prayer is that I have the strength, aptitude, resolve, and means to take the war to the enemy...To me it means the gun that you have with you when the cow excrament self levatates up into the rotating oscillator.
We had a similar term for the break out war that we expected in Korea - Come as You are. Meant that you fought the fight/war with what you had on hand when it started and don't expect any additional help in the near future
GO TO WAR GUNS. It seems so long ago, but feels like yesterday. The M16A2 in my hand and Beretta M9 at my side. For those of us that have seen the Elephant, the weapons we fought with will always come to mind.
But I find that most that are looking for that GO TO WAR GUN have yet to see the Elephant, or never will.
I pray to God that those that have not tested a gun in war never have to. And for those of us that have that we fine peace within as the years fade.
I can still hear the sound of thunder on a clear day.