shield is not only utterly shit but totally pointless if it only lasts for 5 seconds, its also a waste of money. also in survival there is no way you'll last beyond wave 6 as your fighters fly in a pattern where the enemy is always easily able to attack them every time
uni soviet is IMPOSSIBLE to beat as wgen you hit their crystal they recharge it up again (which you cant do), plus they have better planes & weapons & rebuild MILES faster than you can. so it'll be impossible to beat. i just played it for over 30 mins getting absolutely nowhere.