Gandhi and the Congress had announced that the Quit India Movement would commence on 9 August 1942 with a rally at
Gowalia Tank grounds in Mumbai. Nearly all leaders including Gandhi were arrested before that date. However, a vast crowd of Indians gathered at Gowalia Tank Ground on the appointed day. It was left to a group of junior leaders and workers to address them and hoist the national flag. On 14 August 1942, Usha and some of her close associates began the Secret Congress Radio, a clandestine radio station. It went air on 27 August. The first words broadcast in her voice were: "This is the Congress radio calling on [a wavelength of] 42.34 meters from somewhere in India." Her associates included Vithalbhai Jhaveri, Chandrakant Jhaveri, Babubhai Thakkar and Nanka Motwani, owner of Chicago Radio, who supplied equipment and provided technicians. Many other leaders, including Dr.
Ram Manohar Lohia, Achyutrao Patwardhan and Purushottam Trikamdas, also assisted the Secret Congress Radio. The radio broadcast recorded messages from Gandhi and other prominent leaders across India. To elude the authorities, the organizers moved the station's location almost daily. Ultimately, however, the police found them on 12 November 1942 and arrested the organizers, including Usha Mehta. All were later
imprisoned. The Criminal Investigation Department (CID), a wing of the
Indian Police, interrogated her for six months. During this time, she was held in
solitary confinement and offered inducements such as the opportunity to study abroad if she would betray the movement. However, she chose to remain silent and, during her trials, asked the Judge of the
High Court whether she was required to answer the questions. When the judge confirmed that she was not mandatory, she declared that she would not reply to any of the questions, not even to save herself. After the trial, she was sentenced to four years' imprisonment (1942 to 1946). Two of her associates were also convicted. Usha was imprisoned at
Yerwada Jail in
Pune. Her health deteriorated and she was sent to Bombay for treatment at
Sir J. J. Hospital. In the hospital, three to four policemen kept a round-the-clock watch on her to prevent her from escaping. When her health improved, she was returned to
Yerwada Jail. In March 1946, she was released, the first
political prisoner to be released in Bombay, at the orders of
Morarji Desai, who was at that time the home minister in the interim government. Although the Secret Congress Radio functioned only for three months, it greatly assisted the movement by disseminating uncensored news and other information banned by the British-controlled government of India. Secret Congress Radio also kept the leaders of the freedom movement in touch with the public. Reminiscing about those days, Usha Mehta described her involvement with the Secret Congress Radio as her "finest moment" and also as her saddest moment, because an Indian technician had betrayed them to the authorities. ==Post-independence==