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The information on the 80 destroyed M1s is from a US Army report and usatoday and the freelibarary.com. I seriously doubt that all of those souces would have some sort of a unified vendeta against a tank.
There are a few issues with the sources. "Destroyed" does not mean beyond repair. I believe there have only been about 18 Abrams destroyed beyond repair and all of those were from large IEDs exploding from below or from EFPs and/or RPGs hitting the rear area then causing a catastrophic fire that melted down the tank. There is no composite (the US codeword for a Chobamh-like armor, since we couldn't use the British name of it) underneath or on the hull rear or sides, only in the front slope and the turret. The rest of the tanks were damaged, rebuilt, and sent back to units to use. Some most likely became the Aussie M1A1 AIMs, more on that later.
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As for the M1's armour my source is Jane's Combat Vehicle Recognition Guide, Fully-Updated Second Edition by Christopher Foss. It designates the M1's armour as Laminate/Steel to the Challenger I as Chobahm/Steel to the the K1 as Laminate. And for a correction, it lists the T-72's armour as composite/steel. So the M1 has no Chobahm armour.
The problem here is a copyrighted name, Chobahm is the British designation of the composite armor. The US uses their own derivative of it and simply calls it laminate armor, not specifically Chobahm. It is basically the same thing though, just US made. So Jane's is right, and the Abrams does use a Chobahm-equivalent armor made of laminated composites.
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As for the Australian M1s according to www.defence.gov.au,"We're not buying Depleted Uranium (DU) armour or munitions, we are buying an advanced composite armour which is comparable and in some areas better, than DU." looks like someone's information is off so I wouldn't suggest being accusitory.
The Aussie M1A1s are rebuilt, older US M1A1s w/out DU armor. They are called M1A1 AIM (Abrams Integrated Management) Program tanks. They are older tanks totally stripped down to their bare hulls and rebuilt with new or rebuilt components to restore them to like-new (0 hours, 0 miles) condition. They still have the laminate armor of all Abrams, just not the DU armor of later Abrams.
As to why no Challenger IIs have been destroyed in Iraq is simple numbers and how they were used. The US has had thousands of Abrams all over Iraq over the last 8+ years. The Brits have had a Bn of Challys at a time and only in Basrah, one of the quietest areas of Iraq. If the Challys were there in the same numbers, doing the same missions, they too would have similar loss rates. The Chally II and Abrams are pretty much equal in survivability, lethality, and all other areas.
You may just want to listen to some of the guys who have actually worked on and crewed the Abrams. They do know what they are talking about. Just because you read something in a book does not mean it is exactly as the book states it. Experience has its value as well. When you take both the book knowledge and combine it with the valuable experiences of those who have been there and done that, you usually have a more clear picture of what really is.