LONDON--The British Admiralty, abandoning its policy of secrecy with regard to operations against enemy submarines, claimed the destruction of three U-boats today.

The disclosures, along with the Admiralty announcement of the torpedoing of the 5,202-ton British steamer Hronspool and a report in New York that a French tanker, believed the 15,436-ton Emile Miguet, had been found burning at sea, apparently signalized a renewal of the marine phase of the war. Casualties had been negligible during Nazi peace overtures.

With regard to the submarines sunk, the Admiralty said only that some of the survivors were resened.