Twelve British warships anchored at the Spanish-claimed colony of Gibraltar and set off a storm of protest from Madrid. Spain denounced the visit as a flagrant violation of its territorial waters and, while pledging not to use force, said it would take all steps to guarantee its rights. Britain, which had informed Spain in advance, said the five-day visit was routine. Diplomatic sources suggested the Spanish reaction had been whipped up to coincide with a municipal election campaign, the first major test of popularity for the six-month-old Socialist government. Spain has long claimed the British colony as its own.