Wow! That is very helpful, folks, thanks so much for the answers!!
I also had no idea that the Ship List on the right is selectable. What a brilliant interface design! I do wonder how many more gems are lurking in this game as I stumble my way through it!!
Nalgas (fancy name, by the way!!), that explanation clears things up. I'd tried selecting some ships first and then using N+4 as a follow-on, and had no luck with that, but your approach makes sense. As does using the ship selection list!!
Under other circumstances, I use the "L" key judiciously. BUT, in this case, because of an AI Eye defending an AI homeworld, I had to select not just all My Level 3&4 Bombers, but also all my Level 4 Missile Frigates, and my Level 4 Fighters, and my Level 4 Electric Shuttles...
Of course, I ended up losing the game 15 minutes into the battle when 432 Frigates stormed into my homeworld system. I'd gotten greedy and kept my Bombers committed to the homeworld attack. Pretty silly, given that I had all those Level 1 & 2 ships parked back at my nearest friendly planet.
Ah well, I'm still figuring out numerous aspects of the game (this was only the 2nd full game I've completed, to a happy or unhappy end!!). Just little details like Mobile Builders, for example...
Thanks again for the warm welcome to the forum and the great responses. One more reason to recommend this game to my friends!