[@Oak7ree][@Lady Selune] I've seen it too, and I know it's not used everywhere.  But basically, Lt can modify other ranks.  Lt commander is used in star trek, one rank below commander, for example.  So Lt corporal would be about one rank below a corporal.  Lance corporal is also one I've seen.  Look up [url=https://en.m.wikipedia.org/wiki/Ranks_and_insignia_of_NATO_armies_enlisted]NATO ranks[/url] on wikipedia.  It's a pretty good resource, though I can't seem to find Lt corporal there.