Ok, To first answer your question, The Bhishma SK and Bhishma Late were created earlier into the making of the TT, before a proper deep-dive into the Bhishma tanks and their Marks. And I agree with most of your suggestions, and will include/implement these in a TT update soon.
Now per your request, The Arjuns!
Arjun: India’s Desert Archer
Arjun Tech Demonstrator:
One of the earliest photos of Arjun, this shows arjun when it was just a proof-of-concept tech demonstrator in 1989 after consulting with Krauss-Maffei to create a working prototype. The turret looks blocky due to experimentations with composite armor, however the chassis looks near-identical to the production-model Arjun Mk.1.
Arjun Mk.1 Prototype:
The Arjun Mk.1 (P) is one of the first prototypes of the Arjun, being built in 1993, having a more turret closer to the final model now features a raised gunsight, and was key in testing the new 120mm Rifled Cannon, and would lead to the creation of the PPS (Pre-Production Series) Arjuns, PPS-1 - PPS-14.
Arjun Mk.I Early:
The Arjun Mk.1 Early refers to the first limited-production run Arjuns based on the PPS-15, the final prototype and basis of the standard Arjun tank, PPS-15 built 1997 and the production run beginning in 1999. The Early Arjuns still used the sight found on the prototypes although now embedded in the turret 2A4-style and now has properly equipped GEN.1 Kanchan Armor, and now sees the inclusion of the commanders sight and roof MG.
Arjun Mk.1:
The Standard Mk.1 is the regular serial production of the Arjun tanks from 2003-2018, with slightly improved Armor, a much improved gunner sight, and the shifting of the smoke grenades to the rear of the turret, and better electronation of equipment (although this doesn’t really matter in-game), and is now equipped with the SAMHO gun-launched ATGM.
Arjun Mk.I VIRCM:
The Arjun Mk.1 VIRCM is a Arjun Mk.1 equipped with a soft-kill APS system designed by the Israeli-Company Elbit Systems, seeing its smoke launchers replaced with spectral smoke launcher mounted to the front of the turret and now is equipped with a IRCM emitter on the turret as well, similar to the T-90A’s Shtora system or the M1A1 HC.
Arjun Mk.II Prototype:
The Arjun Mk.IA prototype was first seen in 2018, being a Heavily-Upgraded Mk.I tank, seeing the addition of ERA and Composite blocks to the front and sides to the tank, a (TW) mine-plow, a upgraded gun and engine, new electronics, suspension, turret bustle, and GEN.2 Kanchan Armor. However with these additions, the Mk.IA prototype looses the commander’s sight and roof MG.
Arjun Mk.IA:
The Arjun Mk.IA is the most advanced Arjun tank to date, first seeing production in 2019, and is slowly replacing the Mk.I Arjuns currently in service. The completed tank now features a 12.7mm RCWS, a LWS, upgraded commander’s sights, and over 70 additional upgrades to the tank.
Tank-EX:
Tank-EX refers to the Tank-EX program, a military venture to bring India’s T-72 tanks to the new era by retrofitting modified Arjun turrets onto them. Tested in 2002, the program was cancelled due to being strategically unnecessary, expensive, and would prove difficult to preform maintenance on. Interestingly, The Tank-EX programs would see the testing of Israel’s LAHAT missile, however it was also abandoned, replaced by India’s SAMHO.
Karna:
*(Note, “Tank-EX”, and “Karna”, refers to the same tanks, however due to their being 2 variants, I chose to use the names to separate the variants, Similar in concept to how Abrams tanks are called “M1s”, but are also known as “Abrams”.)
The Karna tanks are the parade variants of the Tanks in the Tank-EX program, now seeing the inclusion of rubber tracks, a commander’s sight, and roof MG.
M-46 ACS (Arjun Catapult System):
The Arjun Catapult System is a Self-Propelled Howitzer that is in service by the Indian Army, replacing the previous Vijayanta Catapult Platform. Using a Arjun MBT hull with the turret replaced by the same rearward-facing Soviet 130mm M-46 Howitzer, the Catapult System sees much improvement in its protection and mobility. 40 systems are currently in service alongside the K-9 Vajra SPH.
Here ya go! Again if you have further questions or I mentioned something incorrect, please let me know! And if you want similar explanations about other vehicles/series, do say!