Out of the three "two-faced" civs (US, Canada, Aussie), I have noticed that both Australia and the US have rapid-fire artillery capable of complete devastation in large enough numbers. Out of the Pom-Pom AA gun and the Gatling Gun, I'd have to go with the Pom-Pom. [At this point in time] it has a slightly higher ROF and no reload time. It just keeps spitting out flak like there's no tomorrow. Have a line or two of these at your disposal alongside things to protect them from harm, and the Australians become complete and total lawnmowers.