Basically a military tribunal is similar to a court-martial
or a military trial during a period of war. The rules of evidence that are in civilian criminal trials do not apply.
The President's power to convene a military tribunal comes from the Constitution and international law. International law also includes the so called laws of war. The Manual for Courts-Martial governs trials by court-martial and refers to tribunals as "commissions". The manual provides that, subject to any applicable rule of international law or to any regulations prescribed by the president, military commissions shall be guided by the appropriate principles of law and rules of procedure and evidence prescribed for courts-martial.
The United Nations only requires that military tribunals be "fundamentally fair". Apparently President Bush's order calling for a military tribunal meets the minimum requirements in order to be "fundamentally fair".
Here's one catch. Bush's order provides that the tribunal can only try non U.S. citizens involved in international terrorism. The Supreme Court has also ruled that military tribunals cannot try United States citizens if civilian courts are open, thus excluding one John Walker Lindh.
Here's another catch. Members of the al-Qaeda organization are not considered prisoners of war and therefore do not have protection under the Geneva Conventions. Instead, they are, under international law, considered something called "illegal combatants" and are subject to trial under military tribunals. The United Nations established this precedent in both Yugoslavia and Rwanda.
Okay, so how does a military tribunal differ from that of a courts-martial or civilian trial. Well, for starters, a federal trial is generally open to the public while a military tribunal may be closed. Advocates of the tribunal process say such a setting denies a public forum to the accused.
Next, a military tribunal can be held in a different country than that of the good ol' USA. They can even be held aboard a U.S. naval ship.
Greater security can be imposed over what information is disclosed in a military tribunal as compared to a federal prosecution.
Similar to a court-martial, a military tribunal is composed of military members, usually officers and usually no fewer than five, the minimum number that can sit for a general court-martial.
Unlike a federal prosecution, a person tried by a military tribunal does not have the right to a jury trial.
The tribunal's findings of guilt or imposition of the death penalty does not have to be unanimous. In the case of a five member panel, four members could vote guilty and impose the death penalty.
And last but not least, the death penalty may be imposed immediately. No need for that crazy appeals process.