Battlefield 1

I have added all my individual guides for the codex entry achievements into one massive guide here. Some important notes which I will add also:
- Field Manuals save after being picked up so you can leave the mission without getting worried you need to get it again. There are 66 of them to collect.
- Once a challenge has been completed you can simply leave to game and it will save.
- The Bloody April challenge in Total War seems to be glitched for some people. If it doesn't stay unlocked after completing it simply complete all other challenges and come back to this one to get the Master of Adaptation achievement/trophy.
- Field Manuals have been given separate videos mission by mission in order to help the trophy/achievement hunter following the guide and make it easier on them.

War Story: Friends In High Places
Chapter: Test Flight

To Be Ace - Finish the target practice in test flight.
This is story based and can't be missed.

The Dicta Boelcke - Don't lose the trail during the chase in test flight.
There are 2 times that this will happen. The first will be when you need to just follow the plane a white circle will pop up on the screen. DON'T LOOSE THIS CIRCLE. You MUST stay right next to him otherwise this will fail and you will need to reload checkpoint. The second time he will start flying and using more movement so you need a perfect balance of speed and throttle to make sharp turns. The more that you push forward on the left thumb stick the faster you will go but the harder it is to turn so pull back a little bit to make those sharp turns easier. After the second time this will unlock.

Chapter: Total War
Strategic Bombing - Destroy the fort in Total War.
This will be story based so complete the mission and it will unlock.

Bloody April 1917 - Have at least four bombers survive a bombing run in Total War.
This is actually very simple. Rather then attacking the planes as Wilson will tell you to, head down and destroy the anti air trucks as these will cause massive amounts of damage to your bombers. After destroying them quickly you should have 4 left so if the bombers aren't near the fort by then quickly go kill some planes, however if they are near it you can just sit back and watch the codex pop as they drop the bombs.

Chapter: Fall From Grace
No Man's Land - Reach no man's land undetected in Fall From Grace.
I personally was able to just sprint from start to finish without being spotted but if you would like to tank it more slowly then make sure that you are using your lures which you should be properly introduced to at the start of this mission. Credit to 'Ps4Trophies' for the video guide:

Booby Traps - Use tripwire bombs to kill 2 enemies in Fall From Grace.
From the spawning area follow the road and you will find a box that contains a trip-mine grenade inside it, pick this up. Now that you have the trip-mine, continue down the path and you will see 2 enemies near a fire, these are the guys we are going to kill. Sneak up behind them and quickly plant a trip-mine at each of their feet then run! This should see both blow up and the codex entry will unlock.

France - Defending Home - Collect all field manuals in Fall From Grace.
0:00 - Field Manual 1
0:25 - Field Manual 2
1:05 - Field Manual 3
1:30 - Field Manual 4
2:12 - Field Manual 5

Chapter: Forte et fidele
Gotha Raids on London - Take down the bombers in Forte et fidele.
This is story progress so you won't miss this.

Airborne Cannons - Destroy 10 aircraft within 30 seconds using the stationary weapon in Forte et fidele.
This can be quite difficult depending on how the planes react towards you (took me 6 tries to get it) but this can be started when you get control of the turret on top of the Zeppelin. Simply shoot 10 enemy planes out of the air within 30 seconds of your first kill and this will pop. Enemy ships have sort of a pattern, three will instantly spawn in-front, one will fly past you, a few more will fly in from in-front of you then 3 enemy bombers will fly in, here is my video showing how I got it & I have included another video showing an actual fully detailed guide!

Jousting With Dragons - Collect the Field Manual in Forte et fidele.
0:00 - Field Manual 1

Dawn of Dogfights - Complete Friends In High Places.
Just watch the final cutscene and you get this.

First Solution here. I found most codex entries pretty straight forward, do what it says. The only one that really causes problems is Airborne Cannons. Took me countless tries to succeed. I have another video here that describes where they spawn. It helped me a lot so I thought it might help some others.

The last two missions have Codex Entries for finding all the Field Manuals. I have a complete video with all 6 Field Manuals in this war story. I post the video only once for all 2 mission codex entries:

Field Manuals:

Test Flight

To Be Ace - Finish the target practice in test flight.

The Dicta Boelcke - Don't lose the trail during the chase in test flight.

Total War

Strategic Bombing - Destroy the fort in Total War.

Bloody April 1917 - Have at least four bombers survive a bombing run in Total War.

Fall From Grace

No Man's Land - Reach no man's land undetected in Fall from Grace.

Booby Traps - Use tripwire bombs to kill 2 enemies in Fall from Grace.

Forte et fidele

Gotha Raids on London - Take down the bombers in Forte et fidele.

Airborne Cannons - Destroy 10 aircraft within 30 seconds using the stationary weapon in Forte et fidele.

Dawn of Dogfights - Complete Friends In High Places.

The only one that gave me any trouble was Airborne Cannons

The pinned guide is excellent, but if your a new player Airbourne Cannons is a nightmare. I take no credit for this, this info came from the comments on the main guide, as i had to look around and worked it out I thought I'd put this info in one place.

It's technically not glitched as such, just extremely hard as a MP patch nerfed the AA guns and this carried over into the campaign, so the last 3 bombers that fly right to left simply don't die. I spent 2 hours yesterday and every time I had a perfect run I never shot more than one down.

This fix is for the disc version, obviously play on easy.

*edit* as confirmed by AbsolutioN IX, you can't skip the MP update on the digital version, this will only work on the disc version.

1: Delete the game
2: Install the game and wait for the 22gig patch to install. [edit now a 29gig patch]
3: Boot up the game
4: Refuse the Mp update that the game prompts you to install before playing
5: Without this update the campaign plays as it should
6: Do not play MP until you have it, the game saves a checkpoint per level, so even if your not playing that mission you can restart from check point

I got it 3rd try using this method, hope it helps

*Edit* as confirmed by Ryn0 L this is even simpler if you play offline and refuse all updates before playing:
Video and credit to him:

there is actually not that many codex entries to complete in this mission series as most of it is just flying around in a plane ... either way i made a video guide to help anyone that is stuck :) enjoy

I've previously obtained similarly infuriating Achievements such as Sum of All Zeros in World at War and the asteroid shooting cheev in Dead Space, so it wasn't a lack of skill that kept me from the AA guns challenge. I can confirm that as of Feb 2019 the best way to get this is to have a few other codex entries undone so that Airborne Cannons is not the last one you need. I didn't plan it that way- it was just that I never bothered to get the rest because Airborne Cannons was so annoying.

To note, my "copy" is the digital download that came with the S-model system I purchased back in late 2017. In between then and now, my game had been fully patched due to some frequent Multiplayer sessions.

After reading the solutions above, I purchased a physical disc (early enlister deluxe edition). After returning home, I made a few more fruitless attempts to unlock airborne cannons codex. Finally fed up, I closed out the game (by returning home and briefly playing another game so that I could be sure B1 wasn't still running), then I uninstalled the digital version (while still online), then disconnected from the local WiFi network. After that, I inserted the physical disc I had just bought. At no point did I reset/restart/turn off my console.

After a few minutes, at which point the game was about 33% installed, I was able to play it. None of the multiplayer components had installed, but I was able to go right into the proper level to attempt Airborne Cannons yet again. I also was pleasantly surprised to find that my previously unlocked Codex entries and collected Field Manuals were still present. I switched the difficulty to easy, and I was also able to start right at the 4th part of that War Story, so it wasn't long before I was right back to manning that flak gun and being told what a stand-up man I am. I ended up shooting down the various fighters and the three bombers with no difficulty whatsoever, and before I knew it the Codex entry had unlocked with astonishing ease! Sans multiplayer patch, they practically disintegrated when shot!

So yeah, I can definitely confirm that some multiplayer patch had the effect of rendering this challenge unobtainable, and that one has to uninstall and go offline to have any real hope of unlocking it. Once I finally unlocked it, I then finished the mission (and that whole War Story), went back to the main menu (while B1 was still running in the background), re-connected so as to be back online, then obtained the last few other codex entries in the other levels of Friends in High Places and the Achievement popped as expected.