With a wife and children to support, he aided the World War II effort by working as an electrician at Bethlehem Steel, where he became the first Jewish union representative, and by buying war bonds. He used the $1,500 bond proceeds and $3,500 borrowed from relatives to start a catering company, Industrial Luncheon Services, with a single truck. Unable to buy more trucks after the war, he bought 10 taxicabs and created his own catering vehicles, with sides that rose to reveal stainless steel shelves stocked with sandwiches and snacks--a prototype for today's mobile catering vans. Rosenberg built a multi-state fleet of 200 trucks that served major industrial companies. Soon, he added in-plant cafeterias and a vending operation.