Almost all of Rivera's art told a story, many of which depicted Mexican society, the Mexican Revolution, or reflected his own personal social and political beliefs, and In the Arsenal is no different. The woman on the right side of this painting in Tina Modotti, an Italian photographer and revolutionary political activist, who is holding ammunition for Julio Antonio Mella, a founder of the internationalized Cuban communist party. Vittorio Vidale, an Italian-born Stalinist sympathizer, stands behind them in a black hat. The figures in this painting are an illustration of Rivera's transferring his political beliefs onto canvas. He was an active member of the Mexican communist party, and was friends with Leon Trotsky, who lived with him for seven months.
In 1928, Frida Kahlo becomes a member of the Mexican Communist Party and meets Diego Rivera again. They fall in love. In his fresco "Detroit Industry, North Wall", which he paints in the Ministry of Public Education, he depicts her wearing a red blouse and a star on her breast, distributing weapons for the revolutionary struggle.