In 1942, a 31-story metal building in Dallas was the only U.S. skyscraper of its size built during World War II.

The War Department gave Dallas banker R.L. Thornton special permission for the construction of the Mercantile National Bank Building.

The steel for the building had already been fabricated, so it wasn't economical to halt construction and reuse the metal for battleships and tanks.

Once the tallest metal building in the state, the $1.8 million limestone and brick tower at Main and Ervay streets was designed by architect Walter Ahlschlager, who did Manhattan's landmark Roxy Theater and the historic Peabody Hotel in Memphis, Tenn.

The steel building's signature clock tower was added later.

Renovations to the building and additions on the east side in the '50s and '60s obscured the the original facade on lower floors.

Those additions have now been demolished, and the original exterior is being restored atop the steel building frame.

Originally home to Mercantile National Bank, later Mbank, the metal building has been vacant since 1993.

With 900,000 square feet in the complex, it was the largest vacant office block in downtown Dallas.

The Merc is being rehabbed into 215 apartments with two floors of retail space at the bottom. The first phase opens in February.

A second steel building under construction next door will have more than 150 apartments, and is set to open in late 2008.