Introduction:
Lord Mountbatten was the last Viceroy of India who played a crucial role in the transfer of power from British rule to Indian self-rule. During his tenure, several measures were taken, some of which were highly controversial. Among these, advancing the date of transfer of power from June 1948 to August 15,1947, was the most controversial measure.

Explanation:
1. Background:
- The Indian Independence Act of 1947 provided for the transfer of power to Indian hands by June 1948.
- However, the deteriorating situation in India, with communal violence and political instability, prompted Lord Mountbatten to advance the date.

2. Reasons for controversy:
- Opposition from Indian leaders: Many Indian leaders, including Mahatma Gandhi and Jawaharlal Nehru, were initially against the idea of advancing the date. They felt that it would not leave enough time for the country to prepare for independence.
- Communal tensions: The partition of India was already a contentious issue, and advancing the date further exacerbated communal tensions. It led to an accelerated and chaotic process of dividing the country, resulting in widespread violence and displacement.
- Administrative challenges: The administrative machinery was ill-prepared to handle the suddenness of the transfer. Civil servants and officials had to quickly adapt to new political realities, leading to confusion and inefficiency.

3. Impact:
- Accelerated partition: The decision to advance the transfer of power led to a hastened partition of India, resulting in widespread violence and the displacement of millions of people. The communal riots that followed caused immense suffering and loss of life.
- Incomplete preparations: The shortened timeline did not allow for proper preparations for the new governments, including the division of assets and resources. This created long-term challenges for both India and Pakistan.
- Legacy of violence: The communal tensions and violence that accompanied the accelerated transfer of power left a lasting impact on the relationship between India and Pakistan. It also contributed to the strained relations between different religious and ethnic communities within India.

Conclusion:
The decision to advance the date of transfer of power from June 1948 to August 15,1947, was the most controversial measure undertaken by Lord Mountbatten. It had far-reaching consequences, including accelerated partition, communal violence, and incomplete preparations for independence. The controversy surrounding this decision continues to shape the historical narrative of India's independence struggle.