Soldiers James Cooke, 22, Joseph McCleary, 24, and Martin McGing, 22 of the Irish Guards and Colour Sergeant Carle Selman of the Coldstream Guards, 39, all deny manslaughter in the death of Ahmad Karim.
The Iraqi youth was among a group of four people captured by the soldiers on suspicion of being looters during a patrol in Basra in May 2003.
The soldiers are accused of forcing the prisoners at gunpoint to swim. Karim could not swim and drowned.
The four soldiers appeared for pre-trial arguments last week at a makeshift court martial hall in a giant open loft above a long building at an army barracks in Colchester, east of London.
If convicted, they would be the first British troops punished for causing the death of an Iraqi.
The hearing is expected to last several weeks.
Seven soldiers were cleared of murder last year after their trial collapsed because the judge found that Iraqi witnesses flown to Britain to testify were unreliable.
A third case against seven soldiers accused of killing an Iraqi hotel receptionist is due to be heard later this year.
Three soldiers were convicted in 2005 over abuse of prisoners after one took photos of the abuse to his local film lab to be developed.
Several other defendants were cleared, and none was convicted of sexual abuse, even though the pictures showed Iraqis forced into sexual positions.
Military and civilian police spent three years investigating a friendly-fire incident that caused the death of a soldier, Sergeant Steven Roberts, and an Iraqi man.
But Attorney General Peter Goldsmith finally announced last week that no charges would be brought.