The official wheels

President Barack Obama's new limo is nicknamed "The Beast" It is considered the most secure ever, virtually impervious to chemical and biological attacks and rocket-propelled grenades. (Charles Dharapak/Associated Press)

NORFOLK, Va. — After Barack Obama took the oath of office Tuesday, he rode to the White House in a new custom-built Cadillac limousine that, other than larger windows, isn't dramatically different than the one built for President George W. Bush in 2005.

"Making comparisons to any other car falls apart because there is no comparable car," said Cadillac spokesman David Caldwell.

Specifications and construction of presidential cars are overseen by a small government group; GM is mum on the specifics. And Caddy isn't alone. A look back:

William Howard Taft, with money approved for a presidential fleet, bought a steam-powered, 40-horsepower White Model M touring car and a Baker Electric.

Woodrow Wilson rode in this 1919 Pierce-Arrow Vestibule Suburban Limousine. And though he didn't know how to drive, he bought the car for $3,000 after leaving office. It's now on display at his presidential library in Staunton, Va.

Calvin Coolidge was chauffeured in a 1924 Lincoln Town Car Model L.

Herbert Hoover was a Cadillac man and he purchased his presidential 1930 V-16 after leaving office.

Franklin Delano Roosevelt, despite an assassination attempt in 1933 in Miami, preferred open cars, particularly a Packard Twelve.

But Lincoln supplied FDR with a 1939 limo, nicknamed the Sunshine Special . Built on a Lincoln Model K platform, the V12-powered car transported FDR and Harry S. Truman all over the world.

After the Sunshine Special was retired in 1950, the government obtained a fleet of Brunn-bodied Lincoln Cosmopolitan Limousines.

Though Dwight Eisenhower had a plastic bubbletop fitted to the limo in case of rain, he also went top down in a 1953 Cadillac Eldorado.

The 1961 Lincoln Continental built for John F. Kennedy was modified by the Ohio-based coach builder Hess and Eisenhardt. It was the car Kennedy was riding in when he was assassinated in Dallas in 1963.

Lyndon Johnson also used the car after it was again modified for security purposes.

Richard Nixon rode in a 1968 Lincoln Continental, which was replaced by a 1972 model for his second term.

also served Gerald Ford, Jimmy Carter and Ronald Reagan.

George H.W. Bush had one last Lincoln, a 1989, before Cadillac returned to the presidential fleet in the 1990s.