Families of British soldiers killed fighting in Iraq can bring damages claims against the Government, the Supreme Court ruled today.
Relatives want to sue for negligence and to make claims under human rights legislation.
Supreme Court justices announced today that they can do both.
Families started legal action as a result of the deaths of a number of British soldiers following the American-led invasion of Iraq in 2003.
Their victory at the UK's highest court follows a hearing in London in February.
The decision means that claims can now proceed to trial.
A group of families started legal action as a result of the deaths of a number of soldiers, judges have heard.
Lawyers representing relatives say Corporal Stephen Allbutt, 35, of Sneyd Green, Stoke-on-Trent, Staffordshire, was killed in a "friendly fire" incident in March 2003.
He died after a Challenger 2 tank was hit by another Challenger 2 tank. Trooper David Clarke, 19, of Littleworth, Staffordshire, also died during the incident.
Soldiers Dan Twiddy, of Stamford, Lincolnshire, and Andy Julien, of Bolton, Greater Manchester, were badly hurt in the incident, said lawyers.
Private Phillip Hewett, 21, of Tamworth, died in July 2005 after a Snatch Land Rover was blown up.
Similar explosions claimed the lives of Private Lee Ellis, 23, of Wythenshawe, Greater Manchester, in February 2006, and Lance Corporal Kirk Redpath, 22, of Romford, Essex, in August 2007, lawyers say.
The issues before the Supreme Court were originally considered at the High Court and then by the Court of Appeal.
In June 2011 a High Court judge in London said relatives could bring negligence claims but not claims under human rights legislation.
In October 2012 appeal judges came to the same conclusions.
Relatives say the Ministry of Defence (MoD) failed to provide armoured vehicles or equipment which could have saved lives, and should pay compensation.
The MoD says decisions about battlefield equipment are for politicians and military commanders.
The Supreme Court justices analysed three central legal issues:
:: Whether British soldiers killed during military operations abroad were within the jurisdiction of the UK for the purposes of Article 1 - which protects the right to life - of the European Convention on Human Rights (ECHR).
:: Whether the MoD owed a duty to the deceased soldiers pursuant to Article 2 - which imposes a duty on authorities to protect the right to life by law - of the ECHR.
:: Whether complaints of negligence are covered by the doctrine of combat immunity and whether it would be fair to impose a duty of care on the MoD.
Shubhaa Srinivasan, from law firm Leigh Day, who represents all the Challenger claimants, said: "We are 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.
"We have constantly argued that the MoD's position is morally and legally indefensible.
"The claimants' claims have always been about decisions taken on provision of adequate equipment and training to British troops which are far removed from the battlefield.
"This equipment ranges from the very basic such as GPS devices, to sophisticated satellite tracker systems, which the Americans had available to them.
"It seems incredible that it was often left up to soldiers themselves to buy this equipment as they felt compelled to, so as to better protect their own lives and the lives of those they were responsible for.
"The MoD argument that if they accept a duty of care it would inhibit decisions on the battlefield or undermine morale and military discipline seems to defy logic.
"We argue that morale can only be improved if the Army accepts this duty of care and does everything in its formidable powers to reduce the risks for service personnel on the battlefield."
The Equality and Human Rights Commission deputy director, legal, Wendy Hewitt said: "The Supreme Court's ruling means that human rights protections have been levelled up so that we are no longer expecting our armed forces to fully respect the rights of civilians abroad while not being properly protected themselves.
"From this basic principle it is now up to the courts to decide how this should apply in practice.
"This is not about interfering with the way military decisions are made in the field but how everyone serving in the armed forces is given the protections they deserve."