Halo Wars

Set the difficulty to heroic and activate skulls which will give 50% more health to you and 25% more to your enemy. There's also a skull which makes the ram capacity regenerate faster. The enemies will still die while runned over, but they will be also less vulnerable to shots.

I finally unlocked this achievement after watching the Rooster Teeth's Achievement Hunter video for this, so my tactics were very similar. Since I don't recall hearing the video mention any of the difficulty/skull details, I completed this achievement on Normal difficulty, with the Catch, Sugar Cookies, and Rebel Sympathizer skulls activated. One note before beginning: right before completing the mission, right after getting the achievement, I received the 100/100 Grunts killed notice. However, there were still more Grunts alive inside the base the I killed after receiving this notice. I'm not sure what to make of this, but I am wondering if there are actually more than 100 Grunts in the level.

After many tries, I finally unlocked this achievement (just about five minutes ago, actually). For the first few Grunts/groups of Grunts, I used non-Forge, regular Warthogs to get the kills, pulling guerrilla hit-and-run tactics, trying to allow my Ram ability to recharge (aided by the Catch skull) while minimizing non-Ram damage taken by the Grunts. Most of the time, I tried to use one or maybe two Warthogs at a time, as precision-controlling multiple Warthogs while trying to not allow the trigger-happy gunners to tear too many Grunts to bits can be a challenge. After my Warthogs took too much damage or were destroyed, I allowed Forge to take over. While his Gauss cannon makes short work of Grunts, controlling one 'Hog is arguably easier than controlling a group. Hit-and-run is the key here. The only time I would recommend killing the Grunts as quickly as possible, with little regard to running and allowing Ram to recharge, is when non-controllable Marines are fighting them. Here, you are essentially on a short timer with no control over the Marines and their killing.

Along the way to Alpha Base, do not underestimate the value of the lone Grunt or two. I ended up getting this achievement with about 5-10 Grunts left, but luckily, after watching the video, the value of every single Grunt really occurred to me. When given the choice of the group of Grunts versus the lone Grunt, however, the choice is clear - always maximize your effectiveness and run down the group!

Once you're outside Alpha Base, use a couple squads of Marines to down the barrier, then move everybody back as far as you can from the base. I led everybody except Forge down to near the level's Black Box, but as long as they are out of range of the base entrance, you should be fine. Before you first enter Alpha Base with Forge (or whichever Warthog(s) you choose to use), scout out the enemy. Here, you have a choice: you could either aim for the highest concentration of Grunts for the first strike, or you could aim for the groups nearest the Wraiths, which will most likely be taken out by the ensuing air strike. If you get lucky, one group fits into both categories, choose them as your first target. After you make your first strike, run outside of the base to allow Ram to recharge. After the air strike has gone off, the game is simple: hit-and-run. Always scout ahead before each hit, targeting the largest Grunt groups (preferably the ones in the middle of the base, as the ones behind the pelicans/on the outskirts will stay there), and possibly even behind them to maximize your Ram's effectiveness. While enemies may follow you out of the base, always keep the greatest distance possible between yourself and the enemy unless you're making a Ram hit. After all enemies from the middle of the base are cleared out, use similar hit-and-run tactics for the remaining, stationary outskirt enemies.

Finally, don't get discouraged. I tried for this achievement many times, many ways before finally unlocking it. To those who say it is easy, I'm glad you feel that way. Maybe you caught a lucky break :) To those who call it the hardest in the game, I have yet to get all the achievements in this game, but it certainly took more effort than many of the others. Keep trying, and if my solution doesn't work for you, you may just have to take a different route. The longer it takes, the sweeter it feels to finally see "Achievement unlocked 5G - Everything's Better With Bacon".

I have also embedded Rooster Teeth's Achievement Hunter video here in this solution. Good luck!

I have followed everyones solution for this achievement and none of them worked for me, i did eventually get it but i followed one of RoosterTeeth's Acheivement Hunter videos. The reason the TrueAchievements solutions didn't work for me is because none of them told me to SLOWLY PROGRESS THROUGH THE LEVEL!!! You probably could call me a complete idiot for rushing through it and completely ignore this solution, or you could consider idiots that don't use their heads. So my IDIOT-PROOF-SOLUTION is that you set the difficulty to Normal, turn on Catch skull, and use Seargent Forge throughout the entire level. I know he has a Gauss Gunner (Private Stupid, Super Gunner) which could take out enemies quicker but ignore that. Again I repeat, PROGRESS SLOOOOOOWLY, and take out as much grunts as possible in one ram, and pull back to let your ability recharge, and repeat the above. Aim for the biggest squad of grunts possible. When you get to the end of the level Captain Cutter will call in an airstrike taking out nearly all the grunts you want to introduce to the grill of your warthog. So aim for the squad thas in the middle-most part of the area. This is how i got the achievement, and it was the last one i needed for Ready for The Sequel (100% Completion), and i believe, as most other people do, that is the hardest achievement in the game. So for all my fellow idiots, here you go.

This achievement and level, along with getting the skull, are two of my personally hardest achievements to recieve for Halo Wars.

There are a total of 100 grunts in the whole level so you must kill every other grunt to recieve the achievement unless you're an over achiever. (oh my god a pun!).

Anyways, from the get go I would put the difficulty on normal, and to make things go by faster, however not as necessary, put on the skull which makes special powers (the Y button) return faster.

From there just take Forge and ram, then quickly click behind you into the dark to get away from other grunts. This way you ram a grunt or several, and quicky fall back and retreat so you do not kill any more with the grenadier or gauss cannon. Rinse, repeat.

Three key notes:

Dont take all your warthogs because it will confuse things and they will kill grunts without you knowing.

You may not get it right away, but go through the map a couple times if you're having trouble to learn the locations of the grunts, sometimes there are single grunts standing alone.

When ramming, try and find groups (squads) of grunts so you can score a good 5 or 6 kills with one ram. You must look out for these groups.

Finally, when clearing the base, be careful of your marines not to kill any grunts and also be careful to hit some grunts before the carpet bombs get off, as they may take some kills away.

Hope this helps.

Put the difficulty on either heroic or normal, personally i prefer heroic, then activate the Catch, Rebel sympathizer and Sugar Cookie skulls. Use the normal warthogs when ever possible as the Gauss turret on the back of Forge's warthog rains death upon the grunts. The best strategy is to ram and pull back as fast as possible well your ram recharges. Another good idea is to save after every group of grunts and if you think you could have done better try again. Personally I think this is one of the harder achievements to get so good luck!

I HAVE FOUND THE BEST WAY TO GET THIS ACHIEVEMENT-

Change your difficulty to normal and start up mission 1.
Skip the cutscene and turn on the following skulls:

Rebel Sympathizer
Catch
Sugar Cookies
Emperor

NOW HERE IS THE MOST IMPORTANT PART:

Move your warthog with the Y button. believe it or not when moving with the Y button your warthogs do not attack anywhere near as much as they do when you move normally. You can hit grunts and then drive away from them with the Y button until it has recharged and you will find this achievement 100x easier.

Obviously you will have to progress though the level slowly and when you get to the main base keep everyone away from the base and send forge in by constantly tapping Y wherever you move the cursor and try to keep the grunts away from the air strikes and you will get this achievement alot easier

Got it first time. All i did was set it to normal. throw on the rebel leader, rebel sympathizer, catch, sugar cookies, and emperor skulls. don't use any units except forge's warthog. run up to the big groups of grunts, and back off, then let your ram ability charge and do it again. make sure to not bring any other warthogs or marines, they will take those easy kills you need. just keep rammin' em and u shouldn't have a problem with it. DEFINITELY not the hardest achievement, lolz

I always found it easier on Heroic and don't use Forge as his weapon will most likely one shot the grunts. Know where the enemies are, edge up to the point where the fog of war locates the enemy and ram and retreat.

Remember you're not going for Gold, Par time, Black Boxes or skulls here... Take your time. You will have 1 SOF Heal. You're warthogs may be destroyed in the process but if done right you can get this achievement.

*note. Save the game when the cinematics are done. Or you'll have to go through it every time you restart. lol

Note: I did this on Normal, it gives you three extra grunts to ram than on easy
OK. After completing the mission several times, and not making any progress towards the achievement, I tried several different ways of doing this, and found one that worked for me, and my friend the first time he did it.
What people don't seem to realise is that this achievement can be won WITHOUT SERGEANT FORGE.
In the mission, you don't encounter any grunts until after you rescue your first set of marines, and in doing so you gain another warthog.
USE IT. See, the problem everyone has with this is that Sergeant Forge's gaus cannon wipes out grunts in one or two shots, which means that there's one less grunt to ram. However, the marine warthogs use a machine gun to shoot, and the power is far weaker than forge's turret. This gives you more time, and therefore more grunts to ram, instead of killing them by accident.
You get three of these marine warthogs in the mission, and all three of mine got destroyed by the end, so i just used Forge to ram the last 5 or so grunts.
Note: I did this without any skulls on, but it would help a great deal if you put the skull on that regenerates the y-action faster (in this case, the ramming ability)
Hope this helps

Set the difficulty to normal and turn on "Rebel Sympathizer","Sugar Cookies",and "Catch" skulls. Use all the warthogs at your disposal at the same time to ram grunts. Each time you rescue a marine squad, use the new warthogs with the ones you have. Make sure you ram the grunts at Alpha Base before the carpet bomb, and keep marines out of the base so they do not steal your kills.

I found this easiest on Heroic. Make sure to use the first available warthog and leave Forge back, as he kills enemies too quickly to ram them. Be sure to move all soldiers away from enemies, so they don't steal your kills as well.