Britain's newly appointed Secretary of State for Defence Penny Mordaunt, right, leaves after attending a service to recognise fifty years of continuous deterrent at sea, at Westminster Abbey in London, Friday, May 3, 2019. Royalty, politicians and military chiefs are gathering at Westminster Abbey to mark half a century of Britain's sea-borne nuclear arms program _ though organizers insist they are not thanking God for atomic weapons. (AP Photo/Kirsty Wigglesworth, Pool)

Britain's newly appointed Secretary of State for Defence Penny Mordaunt, right, leaves after attending a service to recognise fifty years of continuous deterrent at sea, at Westminster Abbey in London, Friday, May 3, 2019. Royalty, politicians and military chiefs are gathering at Westminster Abbey to mark half a century of Britain's sea-borne nuclear arms program _ though organizers insist they are not thanking God for atomic weapons. (AP Photo/Kirsty Wigglesworth, Pool)

LONDON (AP) — Royalty, politicians and military chiefs gathered at London’s Westminster Abbey on Friday to mark half a century of Britain’s seaborne nuclear arms program — though organizers insisted they were not thanking God for atomic weapons.

Prince William, Defense Secretary Penny Mordaunt and naval officers and sailors attended the service in honor of Britain’s nuclear-armed submarines and their crews. At least one U.K. sub carrying nuclear missiles has been on undersea patrol at all times since April 1969, a 50-year mission titled Operation Relentless.

The abbey said the service was not a celebration, but a recognition of the Royal Navy’s commitment to “effective peacekeeping.”

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“We can’t celebrate weapons of mass destruction, but we do owe a debt of gratitude and sincere thanks to all those countless men and women, some represented here today, who in the past 50 years have maintained a deterrent, and indeed to their families, who have stood by them,” Dean of Westminster John Hall told the 2,000-strong congregation.

“Those countless men and women played their part, a vital part, in maintaining peace.”

Prince William, who is commodore-in-chief of the submarine service, gave a reading from the Bible.

Successive British governments have backed the nuclear deterrent as helping to keep Britain safe and of maintaining the balance of power.

But peace activists condemned the service, and almost 200 Anglican clergy signed a letter calling for it to be canceled.

Anglican priests were among several dozen demonstrators who held a protest and “die in” across the street from the abbey.

Kate Hudson, secretary-general of the Campaign for Nuclear Disarmament, said the event was “morally repugnant.”

“This sends out a terrible message to the world about our country. It says that here in Britain we celebrate weapons — in a place of worship — that can kill millions of people,” she said.