Another of this artist's comics featuring Achilles confirms that this is a reference to War Thunder. The Achilles in that game, called the 17 pounder Self-Propelled M10, does not have access to the more powerful APDS ammunition that it had in real life, which is why Achilles here in this comic is asking for it. It's worth mentioning that said ammunition was flawed and very inaccurate at first, due to the muzzle break on the 17 pounder cannon among other things IIRC, though the APDS was later fixed.
Furthermore, this comic is a bit outdated as far as War Thunder mechanics go. Previously, AP and APDS did the same (very minimal) amount of damage, but the APDS had the advantage of being much faster and had higher penetration. A few months ago, regular AP ammunition (which the Achilles does have in-game) was buffed massively in terms of the damage it could do, far surpassing APDS to the point where most people prefer to use AP over APDS despite the latter's advantages.
Don't say weird things to a ladyIf you can...Allow me to hear your wish!I want APDS.
Armor-piercing discarding sabot. See comments for more details.My wish is to create "A world where children can be loved".I got it, you want everyone to be a pedophile, right...Also...APDS