[quote=@Oak7ree]...Sissi is a term for a soldier, who uses guerrilla-like tactics, like ambushes, infiltration and such things. There's also a slang term "sissijäynä" (sissi prank) for booby traps...[/quote]
I spent 21 years in the US Army. How you describe the Sissi above, that is what the US Army Rangers do. Rangers are considered the masters of patrolling. Combat Patrols include Ambushes and Raids. They use infiltration as a method for moving into the enemy rear areas routinely. The movie, [url=https://www.youtube.com/watch?v=N51IAYnlNK0]"The Great Raid"[/url] exemplifies what Rangers do. Your definition of the Sissi is quite similar. I couldn't comment on the élan of the Sissi, but if they are anything like Rangers, they are bad ass.

A soldier in the infantry, would be in what type unit in the Finnish language? Would the terms Sissi and Jäger be used to identify a type of unit?