Edit: My guide is now outdated. Rayleigh187 has posted an updated guide. I will keep this guide up however because it is still a plausible way to get the achievement and still has some good information.
There are two mechs that come with the EMP automatically equipped. Those two mechs are the Marauder and the Raider. The Marauder is the closest to being unlocked from the start. From the Web view of the mechs, buy the mech to the left of the starting mech as you will need to get past it unless you plan on using buyable in-game currency. After that there will be 3 mechs to chose from, chose the one above the Berserker (the one you just bought). From there, you will need to buy the next one up, that will be the Marauder and it will contain the ability to EMP enemies.
Note: This achievement was glitchy for me, I had to fulfill the requirements 3 times before it gave me my achievement.
EDIT: If you're finding the process of getting credits too boring or long, then know that the amount of credits for a match is determined by how long you are in the match and if you win or lose (meaning you can afk and still get roughly the same amount of credits). There are also many challenges in the game that give credits .