Why was Aug 15 chosen as the Independence Day for India
On August 15, 1945, Japan surrendered unconditionally.
Because the US dropped two atomic bombs on Japan, killing 250K people in the blink of an eye. Japan had no answer to America’s new genocidal weapon obliterating entire cities in seconds. If it were left to the Japanese army, they would have fought to the death till the last man alive. But they now believed that America would bomb every Japanese and eliminate the existence of the Japanese nation had they continued the fight.
This surrender triggered a wave of joy and celebrations in the US and the UK. They began celebrating 15th of August as VJ Day (Victory over Japan). In America, it was widely propagated as the day marking the victory of the West over the Eastern people.
Which is why Mountbatten specifically chose the 2nd anniversary of VJ Day for the British to leave India. It had this deep oriental symbolism.
But in World War 2, India had no side, as it was engaged in a war of independence against the British. Japanese ravages in Burma notwithstanding, many Prominent Indians like Subhas Chandra Bose fought alongside Japan. They believed India’s best interests would lie. Given this background, India’s acceptance of the VJ date as its own Independence Day and Nehru’s “Tryst with Destiny” speech was a surprise.