London (CNN) -- The families of three British soldiers killed in Iraq can sue the Ministry of Defence for negligence over their deaths, the UK's highest court ruled Wednesday.
The Supreme Court ruling represents a defeat for the Ministry of Defence, which had filed a challenge to an earlier Appeal Court judgment.
The legal firm representing some of the claimants, Leigh Day, said the ruling would force the ministry to recognize "that it owes a duty of care to provide adequate equipment to service personnel engaged in military operations."
The claimants it represents include the widow of Cpl. Stephen Allbutt, who was killed when the Challenger II tank he was in came under fire from another British Challenger II tank on the fourth day of the Iraq war in 2003.
Leigh Day also represents Cpl. Dan Twiddy and Trooper Andy Julien, who suffered severe injuries in the incident. They are known as the "Challenger claimants" for the tank in which they were traveling.
A separate group of claimants are the relatives of Pvt. Phillip Hewett and Pvt. Lee Ellis, who were killed in separate incidents in 2005 and 2006 when lightly armored Snatch Land Rovers hit roadside bombs.
The vehicles were not fully equipped to detect roadside bombs or protect soldiers from a blast, the court heard.
The claimants' negligence claim is based on the argument that the soldiers were not properly trained or equipped by the Ministry of Defence for their deployment in Iraq.
In the case of the Challenger group, the claimants argue that the ministry failed to equip the Challenger tanks with technology that would have confirmed their identity as friend or foe, and failed to provide the soldiers with "adequate recognition training" before they were deployed or in the combat theater.
In the claim involving the Snatch Land Rovers, the claimants say the ministry breached European human rights law because it failed to take measures that it "might have been expected to take in the light of the real and immediate risk to life of soldiers who were required to patrol in Snatch Land Rovers," according to the court ruling.
The Ministry of Defence argued that no duty of care was owed to the claimants by virtue of "combat immunity," because their deaths and injuries were suffered on the battlefield.
But the Supreme Court dismissed that argument, on the grounds that decisions about the provision of equipment and training are made far from the battlefield.
Lord Hope, delivering the majority judgment, said: "The Challenger claims are about alleged failures in training, including pre-deployment and in-theater training, and the provision of technology and equipment. They are directed to things that the claimants say should have been done long before the soldiers crossed the start line at the commencement of hostilities."
Lawyer Shubhaa Srinivasan, of Leigh Day, said they were "extremely pleased" with the decision.
"The highest court in the land has now ruled the MoD, as employer, must accept that it owes a duty of care to properly equip service personnel who go to war," she said.
The ministry's position is "morally and legally indefensible," she said, adding that some soldiers had felt compelled to buy their own GPS devices and other tracking equipment to try to ensure their safety and that of fellow servicemen.
UK Defence Secretary Philip Hammond said he was concerned about the wider implications of the judgment, "which could ultimately make it more difficult for our troops to carry out operations and potentially throws open a wide range of military decisions to the uncertainty of litigation."
But, he said, his thoughts remained with those who were injured and the families of those who died.
"The most important priority is the protection of our troops, and since this litigation started, a wide range of protected vehicles, including Mastiff, Ridgeback, Husky, Wolfhound, Jackal and Foxhound, have been available to commanders to match the most appropriate available vehicle to specific tasks," he added.
According to the Ministry of Defence, the court acknowledged that the uncertainties of war have to be recognized and that the work of the armed forces should not be impeded by the threat of legal action.
One of the judges, in a dissenting judgment, warned that the ruling would make extensive litigation against the British armed forces almost inevitable.