As the other solution said:
"This achievement does not stack - you will not unlock the silver or bronze medal achievements by getting gold"
UPDATE - Here's the other really hard mission "Outback" summed up:
I found the mission "Outback" the hardest in the game. "Kane's Tower" was tough, sure, but Outback took what felt like 10 tries to figure out. There's a REALLY easy way to do it though.
- Blow up the Tiberium Spike FIRST. This ensures the transports cant leave.
- Use one of your engineers to capture the barracks (near the secondary objective), and the other to capture that objective. Build one engineer to capture the Tiberium Refinery up top.
- Knock out all power plants, to kill GDI's defense.
- Once the Power Plants are gone and your refinery is going, SPAM out Missle Soldiers. As many as you can. I had about 20.
- Once you feel you're ready, take one of the transports. Shortly after, the Scrin will arrive.
- At this stage, move everyone to the Evac point. This is where things got a little tricky.
- The timer does NOT start until all three transports are gone from GDI. That means if they blow up or you take them. You only need one to beat the mission.
- The Mammoth Tanks are more of a threat than the Scrin. Try to take a second nuke transport if you can and steer it to the tanks. It sounds crazy but do it and let the Scrin blow it up. Bye bye tanks!
- At this stage, the timer begins. You have 2:30 of hell to go through. Here, it's just luck. Use the Missile Soldiers to obliterate their ground units and your Venoms (hopefully you still have both of them) to kill their air units. It's mostly luck here, as I lost all my units (except the nuke) with 5 seconds left. It was a textbook "OH SHIT OH SHIT" moment.
- Good luck. If you can do this, you're golden for the rest of the campaign.
And now: the grand event: a solution to unquestionably the hardest mission in the NOD campaign, and probably the hardest in the game as well: "Kane's Tower."
UPDATE - There's another thing about this mission. If you act fast enough and you DONT see GDI build an Ion Cannon (which seems like a good thing), you'll get a prompt at the end of the mission saying you failed the bonus objective of, well, destroying the Ion Cannon.
Don't worry. If you don't get a bonus objective prompt, you technically can't fail it. Ergo, if you beat the mission before the Ion Cannon appears and, provided you did the Juggernaut secondary objective, you'll still get the ribbon and the achievement (if this is the last mission for gold) when you go back to the map.
This is a bastard, no doubt about it. As SOON as the mission begins, build a shredder turret and Crane. Also, build a second harvester from the War Factory. Place the turret right below the refinery. Once the Crane is built, construct an Air Tower and Tech Lab. Upgrade your Power if need be.
Build 4 Vertigo Bombers ASAP from the Air Tower. You need these to kill the Juggernauts in the center of the map. Two bombers can take down a Juggernaut, and there are 5 total. GDI does NOT build more Juggernauts, so don't worry.
At the same time, build two Obelisks and put them near the Refinery and Shredder Turret. This is ALL the defense you need for your base. Seriously. Build another Refinery if you can and put it in front of the War Factory, facing the Scrin base. They won't attack it, so don't worry.
At this point if you feel comfortable, SAVE NOW. It only gets worse.
At this point, purchase the Laser upgrade from the Tech Lab, build another Air Base, and get a shitload of Venoms. Venoms are brutal in large numbers, and you can avoid those pesky railguns.
Once GDI rains DEATH on the Scrin base (you'll see a ton of tanks come), build a Emissary and Call for Transport. DONT move it out of your base yet. Build two Obelisks but DONT place them yet.
Around this point, you may find GDI is using Shockwave Artillery on you (a special ability from the "Space Station Uplink" structure). This won't affect you, PROVIDED you keep an eye on it. Shockwave Artillery temporarily knocks out your power and does a decent amount of damage. It will NOT destroy your power plants with one blast, but if you don't repair them, they'll go down. I noticed that they tend to aim the Artillery strike in the same spot (if nothing blows up), so keep that in mind.
GDI will prioritize killing the Scrin base BEFORE they attack the generators, use this time to your advantage. Send your bombers after the Mammoth Tanks and the Venoms against the other vehicles (prioritize the Pitbulls, since they hit back HARD, not as hard as the Mammoths though.)
Airdrop the emissary near the farthest left generator (if you killed the Juggernauts fast enough, it'll still be standing) if it's still there. If not, put it near the next closest one. Deploy the emissary ASAP and make sure any tanks (if they come) don't kill it.
Once it's built, put down your Obelisks. DONT STOP BUILDING Obelisks, you always want two building. You're going to want 10 or so in the same area; an impregnable "wall of death" that kills anything almost instantly.
Just remember to build Power Plants and upgrade them if you need to. Your bound to need more power.
Build a Temple of Nod around now. If you can get one up BEFORE GDI gets the ION Cannon built, you're set. If not, no big deal at this point.
Once your "Wall of Death" is operational and seemingly unstoppable, SAVE. You beat the hardest part of the mission. Now on to the most boring.
From here, it becomes a bit of a stalemate. GDI can't hurt the generators with your wall going, but they still have the ION Cannon. Make sure you have enough Air Bases to send in at least 10 bombers to blow it up. You're sadly bound to lose a few bombers, so be ready to re-build them. DONT nuke the ION Cannon if you can help it. Save those nukes for the Northeast base.
When you have a ton of Venoms, send them to the Southeast base. It has little defense and even less of a threat. Your venoms will probably get shot down by the AA and Mammoth Tanks, but not before you do serious damage. Take out the Crane and Barracks before ANYTHING else. Leave the War Factory, you need this. If you have bombers, send them to take out the powerplants and knock out their defence. As long as only the war factory remains, you're good.
Build more Venoms and secure what remains of the southeast base. Capture the war factory with a saboteur (transport him if you wish) and build a GDI MCV. Build a base, and tech up until you can build three Juggernauts. There's your secondary objective done. Note that these juggernauts, much like the ones at the beginning of the mission, have embarassingly long range. Use this to your advantage if you wish, particularly if the GDI base still has their defenses powered.
Now you have a few options. If you made it this far, you've pretty much won the level. Here's how to seal the deal:
The upper base is EXTREMELY packed in. A nuke will literally level their base. Couple that with the Juggernauts and their embarassingly long range, and you'll do it. Nuke the base, finish off the Construction Yard with the Juggernauts, then just "clean up" whatever is left: Tib factories, war factories, power plants, anything that isn't a defensive weapon.
I spammed Mammoth Tanks with the Railgun and LEVELED them, since they had no power for their massive defense.
It WILL take practice and speed. If you don't move FAST, you have no chance. So long as you knock out the Juggernauts at the beginning fast, and expand into the Alien base (and get your Wall of Death going), you should be fine.