WWII: Sherman. Sure not the best but is was plentiful and versatile.
Cold War: M551 Sheridan. Poorly executed but on paper it was awesome. It could be air dropped, it was amphibious and it was armed with ATGMs. Just amazing flexibility. We need something like this again, but done right.
Modern: Merkava. A tank that has extra space for an infantry fire team is the perfect combination for the modern battlefield.
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