The Russian military has spent months digging in and fortifying its positions in eastern and southern Ukraine. Russian marines during combined exercises with Ukraine's military near Sevastopol in May 2011. "In many cases when they counterattack, this is fundamentally a battle of tree lines," Lee said of Ukraine's advance. "If Ukrainian forces advance and take a tree line, Russian armor moves out and begins to engage that entire tree line at the range of a couple of kilometers. Russian "units are fighting," Lee said.

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