How long after contact does the fighting begin? A lot depends on how much of the enemy capacity each side understands. A single level 2 wizard who knows enough to "pass" as a modern can bewitch guards, control officers, cause wars as nation goes to war with nation because dictators invade their neighbors, etc. Otherwise, the other answers are right that the wizard world can be simply obliterated from miles overhead.

Can a class 2 wizard control someone they can't see the skin of? A tank or an airplane can be easily made so you never see the crew. A soldier with every inch of skin covered may or may not be protected.

I’m voting to close this question because tactics are what happen when in direct contact with the enemy and in response to enemy action. Asking what tactics to use, is entirely dependent upon the specific actions of the adversary. Questions where the answer depends on the actions of individuals are the textbook definition of too story based and are not a good fit for this site.

@DWKraus A few months or about. Enough to learn about mages general capabilities, but not all the intel on the fantasy-landers. Also, these two warring civilizations are different humanoid races, so unless one is a proficient illusion sorcerer, one "does not simply walk into Mordor".

@sphennings Niet. While tacticians have to act based on local circumstances and enemy decisions, many, many elements are independent of these and serve as a guideline. It goes from the obvious "don't attack tanks with rifles" to "being on high ground gives an advantage". This can be seen both in real-world (example here and here) or games like here.

@Tortliena But to get to high ground there needs to be high ground, to not shoot a tank with a rifle there needs to be a tank and rifle in the world. There is doctrine about what a military suggests you do in a specific situation but that doctrine changes over time with the expected adversary, and capabilities. But unless you're asking for doctrine that's not a fact of the world that's how individuals respond to a scenario in the world. Asking how will a fight play out, or what tactics will be used in a fight isn't a question of doctrine its asking us to tell how events will play out.

@sphennings "But to get to high-ground there needs to be high-ground". Then can we perhaps close [this question] for being story-based because "to conceal a magic wand you need to have a wand+magic"? Everything depends on local conditions at some point. You don't build mountain cottages if you lack "high-grounds", you adapt to the environment. The very same happens to tactics, as seen on the marine's introduction to tactics I linked : There are the science of tactics and the art of tactics [...]

[...] Going back to the question, as shown through the answers, there are definitive better answers to such threats, regardless of what individual characters choose. Yes, a genius general wizard can win a battle by tricking with illusions the artilleries and bombers, but their mind-controlling abilities are totally nullified, regardless of what either side do individually : It's an hard-counter to their strongest point. The only missing point I see is the playground the war takes place (mountains, plains, desert...), which is more a lack of details issue.

@sphennings With the question about wands, it's better x_x.

@Tortliena Looking at 3 answers all taking very difficult approaches to the question is a strong indication that the question has many valid answers based on the assumptions they make about the state of the world. Remember that if a question has many valid answers then it's not a good fit for this site. If a question depends on the specifics of an undescribed battlefield to be answerable its not a good fit either.

@2br-2b It's not just the gaze they feel, but the intent behind it as well. Like I said, one has to be a Blank or an experienced wizard to hide from this form of telepathy. And if there is some thin barrier (like a tent) between a sniper and a target... Depends. Apprentices might or might not feel a threat but a more experienced wizard certainly would.

@Sphennings So if a question is difficult, it's opinion-based? I don't get what you mean, I think x). Besides, doesn't look like none of the solutions seems really hard to grasp, nor are they impossible to do at that time period. Otherwise, I do agree more details could be helpful to focus the question and answer more accurately, but not to the point of closure. Anyhow, I think a general strategic point on meta is required about strategy and tactics, it looks like to me there are some misunderstanding why they're not necessarily character-based.

@Tortliena The Q is not about facts of the world but events playing out in the world, in response to characters or organizations within the world. Effectively the Q is asking how a character or organization will respond to a scenario, which by virtue of the scenario and its details existing at the discretion of the worldbuilder, how characters and organizations respond to it will also be at the discretion of the worldbuilder. So it's POB, broad, and a bit too story based, all reasons for closure on this site.

aside from handwavium "its magic" ... why does magic work, WW2 society would most likely be spying and have several labs devoted to learning the secrets and vulnerabilities of the magic folk.

@sphennings Then you're misunderstanding what tactics are, which is what is asked stated in the title and further developed into the body :). In body, the question is not what the organization "would" do, it's what they "can" do, with answers' values being determined by gain to cost. See this meta-post for a similar case, or mine I guess later this week.

@Tortliena If they're asking what can they do then it's an open ended list, idea generation and brainstorming, also not a good fit for this site.

Is a mind hack instantaneous? Can people resist and shout out before succumbing? It makes a HUGE difference. If any wizard farmer can possess a general or a spy instantly and effortlessly, then its hard to see the muggles surviving. At the other extreme, if there's almost always a warning sign, then muggle tech probably wins.

@SeanOConnor Against those who can't weave protective spells, the mindhack is almost instantaneous. On the other hand a duel between two powerful wizards might take many minutes (or even an hour in rare cases). However though, fantasy-landers do use magic almost everywhere, most of wizards are civilians (workers, farmers, artisans and etc.), who don't know any of battle spells and therefore almost completely defenceless.

Can they hack animals?