Nope you can attack twice a turn with the Blitz upgrade, with a full heal between the first and second attack. Essentially it's two units for the price of one, assuming the unit wins the first attack. (I don't know if you get the heal if you choose the retreat option, I never needed to). I defended one of my best city with one veteran archer army and one additional archer unit against 6 roman legion army attacks in one turn, the second archer unit wasn't even needed. Because the unit has a very high survivability rate and the AI kept throwing legion armies at me it was a great way to get a Great General spawn, that archer unit was bad-ass. Built Leonardo Workshop and upgraded it to Rifleman to keep it current too!