An explosion which killed two British submariners was caused by "systemic failures", a coroner has ruled.
Operator mechanic Anthony Huntrod, 20, from Sunderland and leading operator mechanic Paul McCann, 32, from the West Midlands, died on HMS Tireless in 2007.
A self-contained oxygen generator (Scog) blew up while the submarine was under hundreds of feet of Arctic ice.
Armed Forces Minister Bob Ainsworth admitted "avoidable failings" brought about the blast.
Rear Admiral Andrew Matthews, of the Ministry of Defence, added: "We must learn lessons from this."
Coroner Derek Winter said he would write to the government urging action to avoid a similar incident.
Rear Admiral Matthews added: "We had introduced a new self-contained oxygen generator into the Royal Navy, and we believed it was safer.
"But we gave people a false sense of security, and that led to shortcuts in the way we handled things and managed things, and we must learn the lessons from this."
Devonport-based HMS Tireless, a hunter-killer class sub, was sailing under the ice pack 170 miles north of Deadhorse, in Prudhoe Bay, Alaska, when the accident happened.
The two mechanics were trapped in a forward escape compartment by the explosion.
Post-mortem examinations revealed Mr Huntrod died from multiple injuries and Mr McCann of carbon monoxide poisoning.
The mechanics were trapped in a forward compartment by the blast
Mr Winter, the Sunderland Coroner, recorded a narrative verdict, saying that "systemic failures led to the contamination and damage" of the oxygen generators on board "which in turn caused the explosion".
Mr Ainsworth said: "I would like to unreservedly apologise to the families, as I have done previously in the House and in person, for the avoidable failings, for which this department is responsible, which brought about this tragic incident.
"I would also like to pay tribute to the crew of HMS Tireless for their courageous and professional response."
During the seven-week inquest the coroner heard that a batch of almost 1,000 self-contained oxygen generators (Scogs) left in a hazardous waste depot in Devonport were returned to Royal Navy service in 2006.
Mr Winter said it was "a significant possibility" that the Scog which exploded was one that had originally been sent to the dump.
He said: "There was a culture of complacency regarding the risks posed by Scogs and a tolerance of practices likely to increase those risks."
He said at Devonport the practices were much less rigorous than at the UK's other main nuclear submarine base at Faslane, Scotland.
After the verdict Mr Huntrod's mother, Brenda Gooch, said: "In our opinion the coroner's verdict today does not do Anthony's death justice.
"We believe the disregard which the MoD and its employers had shown towards the safety of our son can only be justified as unlawful killing.
"Two young men died through a lack of duty to care for their safety. The complacency across the whole chain of acquisitions, storage and handling is unforgivable to us."
Mr McCann's father, Brian McCann, condemned the Ministry of Justice for not helping them find the funding for legal representation throughout the inquest.
He said: "The MOJ made the decision that they were not going to fund us and did not respond to my letter to meet with them in August last year.
"I, in total, spent 300 man hours studying forms, contracts and different documents. That's not the role of a grieving father, who should be allowed to grieve and have representation.
"I believe the government should make sure each armed forces personnel are given the opportunity to be represented."
Speaking after the inquest Commodore Jake Moors said: "I, on behalf of the First Sea Lord, the entire Royal Navy and the submarine service would like to express our deepest sympathy to Mr and Mrs McCann, Mr Huntrod and Brenda Gooch for the loss of their sons in this tragic accident."