Osama Bin Laden's ex-driver was stopped in Afghanistan in a car carrying two anti-aircraft rockets, a hearing at Guantanamo Bay has been told.
A US army major said Salim Ahmed Hamdan was not wearing uniform at the time of his arrest in November 2001.
Lawyers for Mr Hamdan say he was not an al-Qaeda member and should not be treated as an unlawful enemy combatant.
Separately, the US Supreme Court is debating the rights of Guantanamo Bay inmates to contest their detention.
At the prison at the US naval base in Cuba on Thursday, Army Major Henry Smith told the hearing that Mr Hamdan did not make any serious attempt to resist arrest.
He had two SA-7 anti-aircraft rockets in his vehicle, but not the launching mechanism, Maj Smith said.
The pre-trial hearing is meant to determine whether Mr Hamdan is an unlawful enemy combatant who can be tried in a special military court.
Maj Smith, a prosecution witness, said Mr Hamdan was not wearing uniform or anything to identify him as a soldier, as required of lawful combatants under the laws of war.
However, under questioning from Mr Hamdan's attorney, Maj Smith also acknowledged that some Afghan troops under US command also did not wear uniforms.
Several other witnesses are due to be called, but defence lawyers lost a bid to call alleged 9/11 mastermind Khalid Sheikh Mohammed to testify for their client.
Defence lawyer Harry Schneider told reporters: "People who were actively involved unquestionably are in a much better position than me or you or anyone else in this room to say what Mr Hamdan was."
But a military judge turned down a request, saying the defence should have applied earlier, considering the tight security measures that would be required.
Mr Hamdan, who has been in custody for nearly six years, is charged with conspiracy and supporting terrorism and faces up to life in prison if convicted.
The Yemeni has acknowledged working for al-Qaeda head Bin Laden in Afghanistan for $200 (£99) a month, but denies being part of the militant group or taking part in any attacks.
The hearings at Guantanamo came as the US Supreme Court began considering whether Guantanamo Bay inmates should be able to contest their detention in US civilian courts.
There are 305 detainees remaining at Guantanamo Bay
Two cases challenge the removal by Congress of the "habeas corpus" right of detainees under the US constitution to be heard by an independent judge.
Habeas corpus is a writ which requires a person held by authorities to be brought before a court of law so the legality of the detention may be examined.
The cases have been brought on behalf of 37 foreign nationals who remain among the 305 detainees at Guantanamo Bay.
If the court rules in their favour, indefinite detention under military control could be declared unlawful.
The Supreme Court is expected to decide the case by mid-2008 - its judges have ruled against the US government in two earlier cases.
The government responded both times with congressional legislation curbing legal challenges to the detentions.