To go to war is not a simple matter. Watching too much comics and animations makes us think it were as if taking a dog to a stroll.
1st War is costly.
Having a standby army is one thing. Sending them to the front generates a different kind of cost to the country. From maintenance to supply, they are all expenses that are very expensive to make. Are you as a citizen would really agree with an increase in tax and a possibility that your family/ relatives/ friends/ lovers in the army will not return? If a country wants to go to war it really needs to have the support of the citizens. Otherwise, it is a no go.
2nd A soldier is a human.
Even if they are a trained soldier. Soldiers' job is to complete the objective of the higher management in order to win the war. These objectives are generally consisted of
_ Removing the commanding head of the enemy
_ Plundering the enemy morale to force them into surrender
_ Capturing strategic locations (capital / command centre / a fortress that have a tactical value)
...
They will have to kill enemies to complete their objectives but they are not here to massacre. The mentality of a soldier in the war has only 2 priorities
_ Stay alive while
_ Completing the given objectives
They may be killing people left and right but that's to ensure their comrades and their own survival. After having as much as 10 lives worth of blood in their hands, most of them will have to re-stabilise their resolution and mental strength. Humans are not war machines, they can't kill needlessly and definitely can't kill in cold blood except certain special cases but those special cases will definitely not be appointed any high ranks in the military AT ALL. The Higher-up represent the entire army indeed and since the higher-up is also human beings with needs and wants. They ain't ordering massacre to waste
No 1 their ammunition
No 2 their public image
No 3 their attention
3rd An army is strict.
Maintaining a strict rule of legality and morality is essential when they are in a foreign land. These rules and regulations are what build the procedure and outline how a soldier has to act. In this new world, people easily lose their nerve. These rules are especially important because at least the soldiers know what to act and rely on that. The UN is no more but to ensure a high enough morale and protect the mental state of every soldiers, the army won't allow any INVENTION OF NEW RULE OF WAR. Raping /genocide and any other war crimes will definitely not allowed. They are too busy at hands to change how they would act.
4th Every death counts.
You as a chief / a captain is to bring your entire team back home safely. You will be held responsible for every death you cause, allied or enemy but usually we will favour the survival of our men more than our enemies so bringing all the weapons to counter any potential threats are necessary. MLRs are forbidden but for survival, it may be allowed.
5th Lack of info.
Japan just recently transported to this world. Many thing are new to them and underestimate these unknown thing is the worst possible decision, which is why they went with care and commit to use even forbidden weapons. Just so you are clear. The existence of magic in this world is new to Japan and they don't know how potent those are. It's safer to be mindful and prepared.
