GUANTANAMO BAY NAVAL BASE, Cuba — One Sudanese prisoner is filling his hours until release reading "Decision Points," George W. Bush's memoir on why he quit alcohol, ran for president and approved waterboarding war-on-terror captives.

Another is being home-schooled every other week inside a cell, learning the astronomy, math, grammar, Shakespeare, even elocution, he never got as a child of al-Qaida.

These are the war criminals of Guantanamo Bay. They are four convicts — captured as a cook, a kid, a small-arms trainer and a videographer — kept out of sight of visitors in a segregated cellblock of a SuperMax-style, 100-cell, $17 million penitentiary.

Because each man was sentenced for war crimes by a U.S. military jury, three after guilty pleas in exchange for short sentences, theirs is what the Pentagon calls "punitive confinement." They are "prisoners" set apart from the other 168 captives at what former Defense Secretary Donald Rumsfeld calls "one of the finest prison systems in the world."

Yet, military defense lawyers say the convict cellblock at Camp 5 is especially austere and that their clients are doing hard time reminiscent of Guantanamo's early years when interrogators isolated captives of interest.

Each man spends 12 or more hours a day locked behind a steel door inside a 12-by-8-foot cell equipped with a bed, a sink and a toilet.

They get up to eight hours off the cellblock in an open-air recreation yard, a huge cage surrounded by chain-linked fencing. If recreation time coincides with one of Islam's five-times-daily calls to prayer, the convicts can pray together. If it coincides with meal time, they can eat together.

Once locked in their cells, they can shout to each other through the slots in their steel prison doors troops use to deliver meals and library books.

TV time is spent alone, each man shackled by an ankle to the floor of an interrogation room, always under the watch of a special guard force implementing a Pentagon policy for "punitive post-conviction confinement." That policy is still in flux, says a spokeswoman, Army Lt. Col. Tanya Bradsher, so the Defense Department won't let the public see it.

At 50, Ibrahim Qosi of Sudan is the eldest. Early in his captivity here, Bush-era prosecutors portrayed him as al-Qaida's payroll master. By the time he pleaded guilty to supporting terror last summer, his crime was working as a cook for bachelor irregulars in Afghanistan and occasionally driving for Osama bin Laden and others in al-Qaida.

Now up for release from the cellblock in July 2012, he's passing time with a copy of Bush's best-selling memoir. His Navy defender couldn't find an Arabic translation, so Qosi's learning about the man who waged the global war on terror with the help of an Arabic-English dictionary.

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In a failed bid for clemency, Qosi's attorney, Navy Cmdr. Suzanne Lachelier, wrote in January that, after years in communal custody, living in a POW-style setting, his post-sentencing conditions are "grueling" and "reminiscent for him of the eight difficult months he spent in complete isolation when first arriving at Guantanamo."

But a senior guard who works at the prison said it's far from isolation. "They do get to commune together," said Army Command Sgt. Major Daniel Borrero, whose 525 Battalion pulled guards from the blocks interning U.S. criminal soldiers at Fort Leavenworth to work at Guantanamo.

"It's a prison, ma'am," Borrero said. "I make the assumption they don't want to be here."

The cellblock's youngest is confessed teen terrorist Omar Khadr, 24, and he's on the fast-track to freedom.

He pleaded guilty to war crimes last year in exchange for a promise to repatriate him before his 26th birthday. A military jury sentenced him to 40 more years in prison for hurling a grenade that killed an American commando in a July 2002 gun battle in wartime Afghanistan. But once back in Canada, Khadr's parole is all but certain because he was captured as a juvenile, 15 at the time of the crime.

At his sentencing hearing, a government-paid psychiatrist said Khadr spent his years here "marinating in a radical Islamic community" — memorizing verses of the Quran in the company of captives who got to eat, pray, watch satellite TV and shoot hoops in groups as a reward for good behavior.

Now Khadr's cut off from that group, as a war criminal segregated in circumstances his Army lawyer, Lt. Col. Jon Jackson, says are "horrific and stupid and don't make any sense."

Khadr's father, an al-Qaida insider who has since been killed, moved the family from Toronto to Afghanistan when the boy was in elementary school. So to prepare him for life back in Canada, Khadr's Pentagon defense team is shuttling twice a month to the remote base for attorney-client visits in a compound, Camp Echo.

There, for four days out of five, military lawyers and paralegals are drilling Khadr on a home-school-styled curriculum designed by a Canadian college professor — history, astronomy, math, grammar, elocution.

English is the emphasis, said Jackson, to help him achieve "mature student" status in Canada, a gateway to college admission.

Not so long ago, the al-Qaida convict played Romeo to the Army officer's Juliet.

"He's very serious about his education," Jackson said. "His attitude is positive. There's been a real change in him now that he has the legal matters behind him."

Also on the cellblock are Guantanamo's lone lifer, al-Qaida filmmaker Ali Hamza al-Bahlul, and former weapons instructor Noor Uthman Mohammed. Al-Bahlul keeps to himself, according to military sources, and Noor is just settling in. On Feb. 2, he traded 34 months imprisonment on the cellblock for testimony at future trials about terrorists he knew in Afghanistan.

Theirs is a prison within the sprawling prison system, cut off from the other captives regardless of how good their behavior.

Elsewhere on the base, the military has built a secret lockup for men interrogated by the CIA and suspected in some of the most heinous attacks against America — the Sept. 11, 2001, attacks, the 2000 suicide bombing of the USS Cole off Yemen, the beheading of Wall Street Journal correspondent Daniel Pearl. There are five Uighurs, ethnic Muslims fearing religious persecution in their native China, likewise segregated from the other captives because a federal judge found them unjustly imprisoned.

But Bahlul and Qosi, Khadr and Noor are segregated because they are "serving punitive sentences," says Navy Cmdr. Tamsen Reese, a Guantanamo spokeswoman.

Under the 1949 Third Geneva Conventions, she said, the other captives are "detained under the Law of War only as a security measure" and "should not be subjected to a penal environment or commingled with prisoners punitively incarcerated as a consequence of a criminal conviction."

Once their sentences are over, under Pentagon doctrine, they become ordinary detainees again — put back with the others in a penitentiary called Camp 6, the closest thing at Guantanamo today to POW-style barracks housing.

Or they may leave Guantanamo — if the Obama administration chooses to negotiate their release and congressional restrictions don't hamstring future releases, for example to Sudan, a nation identified as a state sponsor of terror.

That test could come next year. The Sudanese man reading the Bush memoirs finishes his sentence on July 7, 2012.