By 1851, Burma had been greatly weakened, and the British were ready to pounce again. Using a fine of two British ships by the mayor of Rangoon as the excuse, Lord Dalhousie, governor-general of India, sent an ultimatum to rescind the fine, remove the offending mayor, and pay a fine of a one thousand pounds. The Burmese neither wanted nor were ready for a war. They quickly accepted the British demands. But the British officer on the scene, Commodore George Lambert, blockaded the port of Rangoon anyway. On 18 February 1852, Dalhousie increased the demand a hundredfold to one hundred thousand pounds sterling. On 12 April 1852, the British navy invaded Rangoon. King Pagan sent four armies to meet the enemy. The Burmese put up tough resistance at Bassein  and Pegu but by June, much of Lower Burma belonged to the invaders. After the end of the rainy season, in November, the British took Prome, and pushed up to Myede on the Irrawaddy, and took Toungoo on the Sittaung, facing minimal Burmese resistance. In December, Prince of Mindon raised a rebellion against his brother the king. On 20 December 1852, the British issued a proclamation of annexation, taking Lower Burma, up to the latitude running directly east-west across the country to the borders of Karenni states, 6 miles  north of Myede . It took three years to "pacify" the province. Burmese resistance leader Myat Tun, with 4,000 followers, waged guerrilla warfare, repulsing three British attacks before succumbing to a fourth one led by a brigadier general. In 1857, an ethnic Karen leader began another round of guerrilla warfare in the Irrawaddy delta, and was put down only after 8 years.
When did the British take Prome?
the rainy season