This is one of the Leviathans, the cybernetically-enhanced beasts pressed into service by the Chitauri (we assume. They might have volunteered) and armoured to serve as both troop carriers and weapons in their own right. These were created for the film and don't exist in the comics, but in the now established film continuity we know several things. First, these are big, ugly and not very good at navigating the narrow canyon streets of New York. Second, they are as susceptible to Hulk's punching power as the next giant beastie / building / mountain range.