After India gained independence, the Nizam declared his intention to remain independent rather than become part of the Indian Union. The Hyderabad State Congress, with the support of the Indian National Congress and the Communist Party of India, began agitating against Nizam VII in 1948. On 17 September that year, the Indian Army took control of Hyderabad State after an invasion codenamed Operation Polo. With the defeat of his forces, Nizam VII capitulated to the Indian Union by signing an Instrument of Accession, which made him the Rajpramukh (Princely Governor) of the state until 31 October 1956. Between 1946 and 1951, the Communist Party of India fomented the Telangana uprising against the feudal lords of the Telangana region. The Constitution of India, which became effective on 26 January 1950, made Hyderabad State one of the part B states of India, with Hyderabad city continuing to be the capital. In his 1955 report Thoughts on Linguistic States, B. R. Ambedkar, then chairman of the Drafting Committee of the Indian Constitution, proposed designating the city of Hyderabad as the second capital of India because of its amenities and strategic central location. Since 1956, the Rashtrapati Nilayam in Hyderabad has been the second official residence and business office of the President of India; the President stays once a year in winter and conducts official business particularly relating to Southern India.