Mahatma Gandhiji is revered in India as the Father of the Nation. Much before the Constitution of Free India conferred the title of the Father of the Nation upon the Mahatma, it was Netaji Subhash Chandra Bose who first addressed him as such in his condolence message to the Mahatma on the demise of Kasturba.
Ba and Bapu had been interned at Aga Khan Palace, Pune in the wake of the Quit India Movement. It was while serving the prison term Kasturba passed away on 22 February, 1944.

Concerned about Gandhiji, Netaji sent the following message to the Mahatma on Azad Hind Radio, Rangoon on 4th June, 1944.

"...........Nobody would be more happy than ourselves if by any chance our countrymen at home should succeed in liberating themselves through their own efforts or by any chance, the British Government accepts your `Quit India' resolution and gives effect to it. We are, however proceeding on the assumption that neither of the above is possible and that a struggle is inevitable.
Father of our Nation in this holy war for India's liberation, we ask for your blessings and good wishes".

The above message also proves beyond any doubt Netaji's reverence and warm feelings towards Gandhiji whom he had addressed as 'The Father of the Nation'

There have been many queries as to how could Gandhi be called the Father of an ancient civilization like ours. No one is questioning the antiquity of this ancient land.
But India, that is Bharat as we know today that has emerged out of an old civilization is a recent phenomenon. This multicultural multi-ethnic country became a Nation-State owing allegiance to one Constitution, one flag and one Government only on 15 August, 1947. Mahatma Gandhi crystallized about him the living forces of the soil.
So it seemed to a vast millions of Indians, and who saw a Father figure in him and whose `Bapu' he was.