And not the 16th of August or the 13th of September was the date that was decided upon for India’s (and Pakistan’s) independence.
Well, because British India’s last Viceroy (and independent India’s first Governor -General) was a bit full of himself.
The 15th of August, 1945 was the day on which Japan had surrendered—special for Mountbatten because he had been the Supreme Commander for South-East Asia during World War II. In Freedom at Midnight, a book which accords the same position to Mountbatten as the New Testament to Christ, he says:
“I thought it had to be about August or September and I then went out to the 15th August. Why? Because it was the second anniversary of Japan’s surrender.”
On its own, that India’s date of independence was decided such that it would soothe its Viceroy’s vanity might not seem so important. However, when put in context—the extreme haste, even panic in which Britain withdrew from India (transfer of power was originally fixed for June 1948) might have exacerbated the frenzied killings that accompanied Independence—it might have been, tragically so.