PHOTOS: Shell Oil's Arctic Challenger, then and now

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The Arctic Challenger was occupied by Caspian terns while docked in Southern California in 2007.

Royal Dutch Shell's quest to open the U.S. Arctic Ocean to oil drilling, an undertaking that's involved years of preparation and cost more than $4.5 billion, hinges on an old icebreaking barge that sat idle so long it literally went to the birds.

The Arctic Challenger, the troubled centerpiece of Shell's oil-spill response plan, features a remarkable past -- once glorious and, well, not so glorious.

At one point, hundreds of Caspian terns, gulls, cormorants, pelicans, ravens, crows and even an owl turned the 300-foot barge into a giant's bird nest, coating the deck with bird dung and other gunk. That was in California's Long Beach Harbor in 2007, where the downtrodden vessel became a bit of a media celebrity as wildlife regulators raced to save the protected terns and their chicks.

That avian invasion was an ignoble downturn to a celebrated career that began in 1976, when the Arctic Challenger hammered through sea ice off the shores of Alaska and paved the way for the development of the nation's largest oil field.

READ MORE: Arctic drilling: Shell's spill-containment barge was once for the birds