[jester]

YOU ARE WRONG!

Google the following guys,

"Col John Ripley" and "Bridges at Don Ha."

1 man, crawled carrying full combat harness and weapons and satchel charges under a reinforced bridge that could handle TANKs. And he was able to place several charges, enough to drop the spans destroying the bridge. So, it is possible, if one man is able to do it, than I think a team can manage it.

And then the idea of modern mech vehicles with their amphib capabilities.

Sure, the armored vehicles can cross, but who here has traversed water in a armored vehicle? <Marines forward!> its painfully slow, and thus you are an easy target for everything to include slingshots. But, that is not the only thing.

A mech vehicle requires a large support and supply chain. Once the mech amphib vehicles cross, how long can they operate? They'll need fuel, ammo, mechanics to service them, the crews will need food and rest, so how long can a mech force operate if they cross a river and are forced to operate without a supply train? That has been the thing that has doomed most massive military disasters in history! A poor or non existant supply line, it destroyed Napoleon in Russia, the Germans in Russia, the British in the US Revolution, the Americans in the Philipine Campaign and several others. They could not sustain themselves and soon withered and became combat ineffective. Granted, these are major campaigns and a small column of BMPs is a small action, but if they are cut off and do not have the chance for fuel or ammo resuply they will soon be a sitting target unable to withdraw and soon unable to defend themselves.