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The picture you posted is of an
M113 armored personnel carrier (developed in the 1960s), which was mostly replaced by the
Bradley Fighting Vehicle (developed in the 1980s), which is the vehicle you're referring to.
They were only ever designed to resist small-arms fire. They weren't designed to survive heavy weapons. They're better than a truck with benches and a canvas top, which is what these vehicles were replacing - these are personnel carriers, not front-line weapons. But the use of IEDs in Iraq showed that such "supply-line" vehicles required additional armor when such guerilla tactics would be employed.
The
MRAP was developed as a replacement (for HUMVEES) that was able to withstand IEDs and other high-explosives. Interestingly, I believe Bradleys are still being made, while the MRAP program has now been cancelled.
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