You now correctly need ownership of the state of Istanbul. Took them long enough to fix it!

The achievement to invade Gallipoli as Australia is bugged currently. It requires ownership of the wrong state.

It should require the state of Istanbul, which is where Gallipoli is located in real life, however the achievement instead requires ownership of the state of Bursa, which is completely the wrong location.

Knowing this fact, getting the achievement is not too hard.

Below is what worked for me. Not saying it's the best way, just the way I finally got it.

1) As with all games, focus on industry first, with one exception. Your first national focus should be "Political Effort" in order to quickly gain 120 political power, with which you can get someone to start flipping you to Communist.

2) Focus entirely on infantry. Infantry upgrades, artillery, etc. You should get mountaineer divisions ASAP. I also had some marines for river crossings. I used no tanks/motorized. The country is too hilly/,mountainous.

3) Get approximately 60 divisions and enough fighters/CAS to back it up (I had two wings of 400 planes). These can be stationed in Georgia on the border between Russia/Turkey.

4) You can move your troops to the border by shipping them from Australia, to the Naval base north of Japan on Russia's coast. From there they will automatically move to the front line if they are assigned. It will take them a while!

5) Allow for full preparation bonus. By this stage you should be far down the grand battle plan tree.

6) justify and Invade! You should easily take the whole country.

Tips:

• Make sure you're on Regular difficulty, with Ironman and no mods that break ironman!
  
• I used my first 5 Army XP to remove a battalion from the infantry, so they have 20 combat width. Further XP was used to add support divisions, and to buff the mountaineers out to 10 combat width with support.
  
• You'll have more than enough time and equipment to train everyone to Regulars.
  
• If Russia takes the state before you can, you can ask them for it if they like you enough. Or you may have to take some more nearby states and give it to them before they'll hand it over.
  
• You should focus nationally as follows -> Political Effort for Sympathiser -> Then Industrial Tree down until Infrastructure -> Military Factories -> Down to Construction III -> Down to Extra research slot -> Then Army tree, get as much as you can.

Good luck!