Honorable Campaigns will become available at HQ 16. You access it by clicking the orange badge icon on the Alert Tower. It becomes available 3 times a week at reset and will end after 48 hours.
There are 3 campaigns labeled Tank, Aircraft, and Missile. Aircraft campaigns become available after you complete level 5 Tank and Missile campaigns become available after your complete level 10 Tank.
Each level consists of 20 stages and you can only progress to the next level after completing all 20 stages. You can start a new level or start a level you have already completed. Once you start a level, you cannot change it. Also, if you start a lower level you that have already completed, even if you complete it again, you cannot progress. You can do 2 new levels or repeat only 1 lower level that you already completed per campaign reset.
For example, if in Tank campaign, you are at level 15 and start that but cannot complete it, then you are stuck there until the campaign next resets. If you complete it, then you get to do level 16 too, but that is all and you will have to wait till the campaign resets to do more Tank levels. If you find you cannot complete level 15, then you have the option to do a lower level like 14. Once again, if you cannot complete it, then you are stuck. If you do complete level 14, however, you do not get an option to complete another Tank level. Aircraft and Missile levels are each counted separately so you can still do Aircraft levels and then Missile levels following the same rules.
Each campaign, Tank, Aircraft, and Missile, is geared for that hero type. So when you do Tank, you should try to only use Tank Heroes and so forth. However, there is no restriction to do so and you may use any hero in any campaign such as Kimberly in Aircraft. Once you start a level with a certain hero, however, that hero is locked to that campaign. For example, if you use Kimberly in a Tank level, you may not use her again in Aircraft or Missile campaigns.
You get rewards for each level you complete including a chance to level up your hero one level for free up to level 100. It is random, sometimes I’ll do 20 levels and gain 3 hero levels and sometimes I’ll gain none. You gain the most rewards for completing all 20 stages so if you know you cannot complete a certain stage, it is better to do a lower level.
You should use your strongest heroes for each category even if that means mixing in some tank heroes with your squad. I find it is best to simply copy my 3 squads which are squad 1 Tank, squad 2 Aircraft, and squad 3 Missile. I use Violet in my Missile squad because she is higher level and has more stars than Elsa.
While you cannot swap heroes once they are locked to a category, you can swap gear and drone chips. For example, when my Missile team got stuck at stage 15, I moved all my UR gear to that team and also swapped the chips in my drone from Tank to Missile (the chip swapping eventually won’t be necessary once you level up your Drone’s Combat Boost). I was then able to complete all 20 stages.
If you are going to run a lower campaign level anyway, then you can swap in a lower level hero to level it up for free. For instance, if I can’t complete level 15 Missile, then I can do level 11 and swap in Elsa for Violet to give Elsa a chance to level up for free.