Backspace selects your secondary weapons or stores, if loaded. This includes cannons, rockets, bombs, fuel tanks, troops, and supplies. If you go to setup on the clipboard, you can see what the key and button mappings for the various commands are.
Offline isn't a campaign or singleplayer game type. It's pretty much good for practicing gunnery and bombing, flying various aircraft etc outside the chaos that is the Main arena. Town buildings, hangars, gun emplacements etc automatically regenerate over a period of time, regardless of settings. These are all part of the more dynamic online style of play, and, while all can be destroyed, won't necessarily stay down. Anyway, there's no way to pause or save offline play. It's pretty much just a practice range.
If you subscribe to the game, ($14.95 a month for unlimited access to all of the arenas/events), you can request, and be assigned a trainer (there's a separate arena dedicated to training, as well as an actual living breathing training corps made up of players [some of whom have been doing this for a looooong time]), and receive basic instruction from them. It's pretty impressive.
