What does a "military attache" do?

I have been enjoying reading Those Angry Days, by Lynne Olson. In 1937-1941ish, the United States was embroiled in the debate between those advocating intervention in Europe and those who insisted that America must not be drawn into another European conflict. According to the author, many Americans believed that the United States had been suckered into World War I and that the gathering storm in Europe was a direct result of harsh provisions in the Treaty of Versailles. The mood was essentially that Britain and France had treated Germany poorly at Versailles and that the resulting German aggression was their own fault.

Anyway, Olson mentions that Charles Lindbergh (who strenuously opposed intervention) visited the Luftwaffe in Germany. He was escorted by the US Military Attache in Berlin. There was also a German Military Attache in Washington. While the two countries were not at war (and many Americans sympathized with the German cause), why would they have military guys in each others’ capitals. Both attaches provided important intelligence to their home countries during this time. The German attache (accurately) reported that America was nowhere near a war footing and that Hitler could invade as he pleased without concern for American reprisals. Similarly, the American attached reported that the Luftwaffe was the most superior force in the air and that attacking Germany would be a losing battle.

Why would Germany and the USA allow these guys to roam around?

Diplomatic immunity?

You pretty much answered your own question. Military attaches are usually military officers serving as diplomats and advising the Ambassador on military affairs.

Diplomatic immunity does not protect the diplomat against being evicted from the host country as a persona non grata, so the question is valid. My take on the OP’S question is that the sending and receiving of military attachés was, and still is, considered to be part of the “normal” diplomatic relations between two countries, both allied and non-allied countries. The host government is usually very much aware of the thin line between the attaché’s reporting and espionnage, but as a matter of diplomatic courtesy (not international law - under international law, the host country is free to evict foreign diplomats any time it chooses to) these attachés are not declared persona non grata unless they really overstep the line.

Of course, if you chuck my military attaché out, then youse is surely going to be on the next plane home.

The military attache at an embassy does pretty much what you would expect. He liaises with the local military. The office is usually staffed with DIA folks, so there’s a bit more to it, obviously; they’re also there to gather information on local military strength and operations.

I suspect these days the military attache is primarily an arms salesman.

  1. They wanted their own guys to be allowed to roam around.

  2. Since diplomats often double as spies, excluding all such spies would have meant not having any diplomats of the other country close-by.

Or purchaser.

Well, that’s what I mean, though. What benefit is it to the US (of 1937) to have a German military guy wandering around? Why would Germany want a US guy wandering around? Does the German guy show the Americans how they might be more effective in some situation? Does the American observing the Luftwaffe learn some ideas on better techniques to run an air force (like I might learn to be a better teacher by observing a colleague teach his/her class)?

Now, I can see why close allies conducting parallel or joint operations would need liaisons in each others’ camps, but I don’t see why active or potential adversaries would tolerate this.

Generally it’s a good idea to have as many pipelines open as possible. Information inevitably flows both ways. If the American guy observes German preparation, et cetera, he also by his reaction betrays what his government thinks about it – very valuable stuff. If he overhears useful conversations, his own conversation can’t, human nature being not infallible, avoid leaking information about attitudes, at the very least, at the highest circles of his government.

Furthermore, generally if you know someone is spying on you, and they don’t know you know, you don’t eject them at all. Such a person is a valuable asset, because you can feed him all kinds of bullshit and know it is going home burnished with a high level of inherent trust because it’s secret stuff that comes from their own spy, ha ha ha. It’s one thing if the German Ambassador solemnly laments at a state dinner that the latest Panzer factory is late on deliveries – that old bugger would lie with a straight face to his grandmother about what he had for breakfast – but if you can “accidentally” let the Ami Air Attache see a factory in disarray, and overhear a very senior colonel angrily yelling into his phone about some appalling four-month delay in delivery – well, the latter does a much, much better job of delivering the perception you want, because your enemy helps deceive himself. When it comes to information and disinformation, the single most valuable asset to yourself or to your enemy is a trusted pipeline. You leave the pipeline in place because you hope to profit by it. Your enemy lets you leave it in place because he hopes to use it against you.

Yes, it’s a hall of mirrors kind of thing.

I would suspect that in 1937, two years before the invasion of Poland, Germany may have still been considering America as a potential ally, or thought that showing them the vast quantity of military might might deter America from entering the war on England’s behalf (as you mentioned), since our own military was in shabby shape at that time. Roosevelt was very reluctant to be on a war footing right up until Pearl Harbor, and hearing reports of Germany’s mechanized infantry and large, trained air force would reinforce that. Why America would allow a German officer to view America’s lack of readiness escapes me. America was still in the throes of the Great Depression in 1937 and manufacturing had not yet recovered.