If you have seen underwater footage of the sunken RMS Titanic, and ever daydreamed about what it would be like to walk the deck of that drowned wreckage, a stroll on the SS United States may be as close as you can get.

The SS United States -- the rusted and dilapidated cruise liner that's been moored on the Delaware River for 17 years -- is not open to the public. The best view available is from several hundred yards away, in the cafeteria of IKEA across Columbus Avenue.

David Macaulay, the author and illustrator of bestselling books about engineering and architecture, is one one of the very few people to have walked the decks of the SS United States at the height of the ship's glory and at the end of its life.

Since 1974, Macaulay has been making complex design and construction understandable to children and, by proxy, their parents. In his previous books, including "Cathedral," "Pyramid," and "The Way Things Work," he draws cross-sections and exploded views of buildings and objects, teasing out perspectives and details impossible to see otherwise.

For his next project, he started thinking about the history of invention itself, quickly realizing that topic was more than he could chew. So he settled on shipbuilding.

"I wanted to focus on something that would represent the culmination of all this technology," said Macaulay, looking up the port side of the 990-foot ship. "It was a way of consolidating all this random information that seemed to be getting out of control. I was buried under it. I loved it all, and couldn't think of a reason to make a book about it. I needed to tell a story of some kind."

The story he found was his own. Macaulay sailed on the SS United States in 1957 when his family immigrated to America from England. He was 10 years old.

SS United States brought Macaulay to U.S.

At the time, the ship was one of the most luxurious passenger ships afloat. The first-class dining hall had 30-foot, domed ceilings and a raised bandstand for in-demand orchestras. Alfred Menconi even released an album of popular medleys called "Let's Dance on Board the SS United States."

Now, the ship is gutted. Everything that could have been ripped out, has been. Only the infrastructure holding up steel deck floors remains. Flaking paint and rust cover everything.

"This is as lavish as the space got, in terms of luxurious double height," said Macaulay, standing where Meyer Davis would have presided to conduct his orchestra.

Aside from those double-height ceilings and glassed-in promenades stretching for hundreds of feet, there is little about the interior of the SS United States that looks glamorous. Macaulay has the eye of an engineer, not an interior decorator. He came to see the exposed steel infrastructure of the lower decks.

"You're seeing the grid of columns that goes throughout the whole ship and through all the decks," said Macaulay with a small flashlight (the generators had frozen). "It's like any building, except the foundation floats under it all."

The ship was designed by naval architect William Francis Gibbs, who grew up watching ships being built and launched at the Philadelphia shipyards. He always wanted to make the fastest, strongest ship possible. The SS United States was his opus. He built the hull and lower decks of steel, and the entirety of the upper decks is aluminum. After 40 years of disuse, the bulk of the ship is dripping with rust, but the banisters to the bridge still retain their aluminum shine.

The aluminum made the ship lighter, and its powerful engines made it faster. It still holds the record for the quickest crossing of the Atlantic.

The aluminum also makes the ship fireproof. Nothing flammable was allowed. The exterior decks were surfaced with clay, not wood. No carpets were allowed to be laid inside. Instead of classic maritime hardwood, all the furniture and fixtures were made from aluminum.

Some of those pieces are now on view at the Independence Seaport Museum at Philadelphia's Penn's Landing, including art deco clocks and lamps, original deck chairs, and signage, all made from aluminum.

"All textiles are non-flammable, and there was no wood," said curator Elizabeth Lewis, pointing to an aluminum stateroom chair upholstered in orange fabric. "In fact, William Francis Gibbs wanted a Steinway piano in aluminum. But the Steinway company convinced him that what they gave him would not burn down."

Lewis is a member of the SS United States Conservancy, an organization that literally saved the ship from the scrapyard two years ago. Now that it has the ship, the conservancy needs to figure out what to do with it. It is hunting for a developer and a good idea -- maybe a retail and restaurant destination, maybe a museum, maybe a unique housing development. It is also hunting for money; it costs the conservancy about $60,000 a month to dock the behemoth.

Book will cast a new light on old ship

"We're excited because David, we hope, will bring new attention to the cause," said Susan Gibbs, the president of the SS United States Conservancy and the granddaughter of the ship designer. "The book will come out in 2015, so our challenge is to make sure the ship is still with us be the time the book comes out."

To write and illustrate that book, the 67 year-old Macaulay is doing research by scrambling around the derelict ship like a 10-year-old boy playing hooky from school: climbing around the shafts of the engine room and spelunking the catwalks of the smokestack funnels. He knows exactly where the water-distilling system is, how the turbogenerators produced power for the electric ovens in the galleys, and how the engine's chilling pipes pushed cold air into all the cabins.

"What you would be doing in your cabin is not lowering the temperature, but turning up the heat to get the cold air to be more comfortable," said Macaulay. "Kind of the reverse of how you might think it would work, but that was the system at the time."

He regrets that he did not exhibit this kind of curiosity when he was still a boy. At 10 years old, living on the ship for five days, he was more preoccupied with coming to America than with the ship taking him there.

"This is so sad. The stuff that would have triggered my imagination -- it's didn't happen with that machinery. I'm a little surprised," said Macaulay, standing on the ship's bridge where the compass, steering wheel, and radio would have been. "I'm filling in gaps that I didn't realize existed -- and they are huge. I'm learning about stuff I really should have learned then."

When Macaulay looks at the bones of the ship, he sees generations of inventive engineering coming together into a powerful display of speed and pride. That's the real story he wants to tell.