This is hard, but doable. I did this on the first three areas the machine gun was my favorite gun and I saved all grenades pretty much till the whale. I recommend not shooting while you are in your vehicle. If you die just take your hand off the controller and wait to press to immediately exit your vehicle. I reset if I accidentally killed someone or shot bullets with the vehicle so i wont be angry at the end of the adventure. While you are stationary and shooting buildings you won't automatically be place in your vehicle. An extra life is also given at 300,000. I received this near the middle of area 3.
Here are my helpful hints.
Area 1: The mortars you see in the beginning I flanked them on the right when the time was clear and shot them machine gun then collecting the grenades they dropped to add 10 to my arsenal. Clear the area till you get to the suicide bombers. Up above are 2 towers. Stay back till you see maybe a small corner of the towers. Switch to flak cannon. If you stay at the bottom of the screen the towers bullets shouldn't hit you, but the flak cannon will hit them. Clear those out then move a little for the 2 tanks that come. I used the flak on them too. Clear the two towers after the bridge the same way you did the previous 2. When that area is clear move the the end of the bridge without leaving it. If you do this you can see the gate that needs to be destroyed. Shoot it with the flak till it's destroyed. If done correctly you don't need to face the guys that spawn here.
Area 2: This involves being slow. Machine gun all guys coming out of building without moving till the last one has spawned. Don't want any guys coming behind you. Flak cannon buildings in which suicide bombers come out later. This part got me killed once. There are towers that having homing missles. There are points where you can flak him and not get shot, but usually I try and dumb 1-2 grenades on this tower on the far right of the base.
Once the base is clear you'll come to a helicopter drop off. Just machine gun the mortars picking up there grenades and shooting the guys coming out of the helicopter and the one tank coming from the left.
The path on foot is simple if you know what to look for. Watch out for the suicide bombers in front and above you. Now some guys will come up from behind you. I stopped this by just doing a sprinkler move with the machine gun behind me each time I cleared an area. Clearing the end of area 2 is simple most of the time. I just did a big sprinkler move shooting the left side of my screen watching for the tank rockets. When it came clear I threw a grenade at it and just kept mowing down the guys on the left.
Area 3: This is pretty much the same thing as area 2 take it slow. Use the flak cannon on the towers before they have a range on you so on and so forth. I'll skip to the whale. The green blob is invulnerability. I'd use this when you first start fighting the whale because you don't have much time to rush for it when you are hurt. *Rolling with " will be your saving grace. It will help you dodge the whale machine gun and rocket waves. Stay at the back end of the screen while fighting it. By this time you should have all your nukes and about 25 grenades. Feel free to let them all off on the whale. What I did when the the whale was in the water and not on screen was do a sprinkler move behind me because 2-3 men on foot will always be coming after you. This clears them out. If you dodged the machine gun and rockets and the guys coming at you the whale will fall eventually netting you the achievement.