Boaters must adhere to a 100m exclusion zone today
Boaters are being warned to steer clear of an American nuclear submarine which will visit Portsmouth today.
USS Boise, a Los Angeles class attack submarine, will stay at the naval base until Monday 12 July.
Police boats will accompany the submarine during her transit into and out of harbour to enforce the requirement that other craft must keep at least 250m away.
A 100m exclusion zone will be enforced around the submarine while she is alongside in the naval base.
Boise, which is 110m long and cost around $900 million, is powered by a single nuclear reactor and carries Harpoon and Tomahawk missiles as well as torpedoes.
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She displaces 6,000 tons on the surface and 6,900 tons submerged and has a crew of around 130.