LONDON (Reuters) - Britain said on Friday it had awarded Rolls-Royce a 9 billion pound ($11 billion) contract to design, make and provide support services to nuclear reactors that power its fleet of submarines.

The eight-year deal will strengthen the Royal Navy's continuous at-sea deterrent - under which at least one nuclear-armed ballistic missile submarine patrols the seas at all times - while also boosting the AUKUS defence pact with the United States and Australia, Britain's ministry of defence said.

The new contract, called Unity, streamlines previous ones, incentivises cost-efficient production, and would support work on the Dreadnought class of nuclear submarines, it added.

"This investment in Britain's defence will deliver a long-term boost to British business, jobs and national security," Defence Secretary John Healey said in a statement.

"This deal ... will support high-skilled UK jobs who equip the thousands of submariners that keep us all safe," Healey added, ahead of a visit to Rolls-Royce's nuclear reactor production facility in Derby, central England.

The Unity contract is expected to create 1,000 jobs and safeguard 4,000 others, the government said.

($1 = 0.8119 pounds)