During the Russo-Japanese War, countries that were not directly involved in the war, such as the United States, Germany, and France, sent military attachés and observers to keep an eye on the fighting.
Military attachés are like spies, but they are legal and have permission to gather information. They wear fancy uniforms and are usually officers in their own country's military. Their main job is to gather information about the other country's military, such as their strategy, tactics, and weapons, and report back to their own country.
Observers are people who are there to watch the fighting, but they do not have the same purpose as military attachés. They are more like reporters, taking notes on what they see and then sharing that information with their own country.
So during the Russo-Japanese War, military attachés and observers from countries like the United States were there to gather information about the fighting and report back to their own governments. They were like secret agents watching the war from behind the scenes!