On the main menu select Skirmish
Change your Home town/Civilization to British (London) (The flag Icon next to your gamertag)
Select Deathmatch
Change starting age to Post-Imperial Age
Start the game and enter the cheat code: Nova & Orion
Select the flag icon in the bottom right corner of the screen (next to the mini map)
Choose the Land Deck
on line IV Select the 2nd option (Picture of a cannon)
This will deliver 2 cannons to your Town center and will pop the achievement.
Enter cheat code speed always wins to speed this up a bit.