SYDNEY (Reuters) - Julian Assange is en route to a courtroom on the Pacific island of Saipan where he is expected to plead guilty on Wednesday to a single criminal charge in a plea deal that will see him walk free and return home to Australia after a 14-year legal odyssey.

WHERE IS SAIPAN?

Saipan is the capital of the Northern Mariana Islands (NMI), a U.S. commonwealth in the western Pacific which begins roughly 70 kilometers (44 miles) north of Guam and stretches across 14 islands.

Like territories such as Guam or Puerto Rico, the Northern Mariana Islands are part of the U.S. without the full status of a state. Residents are U.S. citizens but cannot vote in presidential elections. Crucially, some, like Saipan, also host U.S. district courts.

Assange will appear in court at 9 a.m. local time on Wednesday (2300 GMT Tuesday)

WHY IS ASSANGE HEADING THERE?

U.S. prosecutors said Assange wanted to go to a court close to his home of Australia but not on the continental United States.

Saipan has the advantage of being relatively close to Assange's home of Australia, roughly 3,000 km (1800 miles) south. Hawaii is more than twice as far away.

"He has to front up to charges that have been brought under U.S. law," said Emily Crawford, a professor at the University of Sydney's law school.

"It had to be U.S. territory but it had to be the U.S. territory closest to Australia that wasn't a U.S. state like Hawaii."

SAIPAN AND THE UNITED STATES

After time as a colony of Spain, Germany and then Japan, the United States took control of the island in World War Two after the Battle of Saipan in 1944.

After decades under U.S. control, residents in 1975 voted to join the United States as a territory.

The Northern Mariana Islands elected a delegate to the U.S. House of Representatives for the first time in 2008, but the delegate has no vote in Congress.

WHAT HAPPENS NEXT

U.S. prosecutors said Assange has agreed to plead guilty to a single criminal count of conspiring to obtain and disclose classified U.S. national defense documents. He will be sentenced to 62 months of time that he has already served. If the judge approves his plea, Assange is expected to return to Australia after the hearing, U.S. prosecutors said.

(Reporting by Lewis Jackson; Editing by Sonali Paul)

By Lewis Jackson