DU Hull Inserts are somewhat of a Red Herring on this topic, as most models of M1A1/A2 have little evidence to support. The main issue is that, along with the turrets, the AUS concurrently upgraded hulls with heavier composite compositions in the M1A1, M1A2, M1A2SEP. They did this while also reducing systems weight and improving material sciences.
I would like help consolidating clean sourcing on the following longstanding issues:
All M1 Series Tanks
Off Center Turret
Turret Ring/ Mantelet Shield
Needs to be volumetric to accurate simulate already in game visual armor thickness.
Mantelet shield implemented incorrectly.
Incorrectly Modeled Armored Fuel Tanks
The armored lining needs to entirely enclose each of the forward fuel tanks, and potentially needs a Kevlar component on the driver’s interior.
Integrated Kevlar Lining
https://community.gaijin.net/issues/p/warthunder/i/BcMSgWYhwd5k
M1A1/M1A2 Variants
Upgraded Non DU Hull Composites/ Additional Armor Insert Weight
The M1A1 Received a weight increase in its frontal hull composites, yet protection remains the same post M1IP in game.
“Frontal Protection” with improved “Turret Side Protection” is debated as terminology a lot, this reference chart clears it up.
And in line with the improved M1A1 Hull

Weight Increases
Upgraded DU Hull and Turret Inserts on the Late M1A2SEP/M1A2SEPv2
https://community.gaijin.net/issues/p/warthunder/i/YCmfAEiaPZSq
Upgraded Suspension
https://community.gaijin.net/issues/p/warthunder/i/nMSA2BTBlnFg