Codeword Cromwell, an invasion patrol, and an uncertain mine

On 7 September 1940, the codeword Cromwell warned of a suspected invasion of Kent and sent Galatea on an overnight patrol in the Dover Strait. She found no invasion force, but at dawn struck a mine off Sheerness and spent three months in dry dock. The mine's origin remained uncertain because it lay outside the expected field. It may have been enemy-laid, or a British mine may have broken free. The patrol shows how invasion alerts sent ships into waters already complicated by defensive mining and bad September weather.