Experimentation works. But I cannot get it consistently. By holding down shift and then pressing one of the top row letters I can get the fleet to spawn, but I cannot get it to do so consistently. I can get it to happen by holding shift and then pressing each key multiple times until finally a fleet does spawn. AFter that fleet does, holding SHIFT-T seems to clone it, so you can give yourself a ridiculously massive and honestly non-fun arnorian fleet.
Again, I have ultimate edition, so I don't know if this is different than other editions, but it's a fun thing to use. Also CONTROL-Y appears to force a mega-event to happen, and I haven't seen that posted very many places either.
Any thoughts on this would be welcome. I would really like to figure out what the conditions are to make the fleet spawn consistently.