Complex sentence: The tanks were launched from points upstream from their objectives, to take account of the Rhine's strong current, mats at the objective points (carried across beforehand by LVTs) allowed the DDs to climb the steep, muddy banks of the river.
Split into simpler sentences: The tanks were launched from points upstream from their objectives, to take account of the Rhine's strong current. Mats laid at the objective points (carried across beforehand by LVTs) allowed the DDs to climb the steep, muddy banks of the river.