Significant steps have been taken to improve the army's Warrior vehicles in the wake of the deaths of six soldiers in Afghanistan, a coroner said today, as he ruled they were unlawfully killed.

Sergeant Nigel Coupe, 33, and Warminster-based colleagues Corporal Jake Hartley, 20, and Privates Anthony Frampton, 20, Daniel Wade, 20, Christopher Kershaw, 19, and Daniel Wilford, 21, all died when an improvised explosive device (IED) detonated under their Warrior in Helmand Province on March 6 last year.

The vehicle was patrolling with another Warrior when it was blown up about 25 miles north of the capital of Helmand, Lashkar Gah, bringing the biggest single loss of life for British forces in Afghanistan since an RAF Nimrod crash killed 14 people in September 2006.

An inquest at Oxford Coroner's Court has heard that no other vehicle of its type was designed to withstand a blast of its type, but that since the tragedy, improvements have been made to Warriors.

Giving a narrative verdict, Oxfordshire coroner Darren Salter said: "This of course is a tragic loss of these six soldiers and these young lives.

"At least it is very clear from the evidence of the two pathologists and the evidence of those who witnessed the strike that they did not suffer.

"It also follows that there was nothing that their comrades could have done to rescue or save them."

Sgt Coupe, a member of 1st Battalion The Duke of Lancaster's Regiment, and his comrades, all members of the Yorkshire Regiment's 3rd Battalion, based at Battlesbury Barracks, died of blast injuries caused by the explosion.

Mr Salter told the court: "I am not going to second-guess decisions of commanders in a courtroom today, that is not the purpose of an inquest.

"These are experienced commanders who took decisions on the ground, balancing the risks and exercising judgments."

Outlining the events that day, he said: "The six soldiers were therefore unlawfully killed whilst on active service."

The inquest heard that improvements have been made to Warriors since the incident including better armour, burst resistant fuel tanks, better ways of getting in and out in emergencies and improved fire detection and protection systems.

The court was told that eight new fuel tanks have been fitted so far to the vehicles that are being used in Afghanistan, with 21 more due to have the upgrade, and the coroner said that "significant steps" had been completed in making improvements to the vehicles and there was no need for a formal report under his powers because he was satisfied the areas of concern had been addressed.