When the Navy began to de-commission ships, Pownall left the military and joined his wife and two daughters in LaJolla, California. He decided to go into business for himself, found a partner, and launched a paper-box manufacturing company. Within months, the company was out of business.

Pownall became a salesman for a steel warehousing company, selling everything from steel to ship hulls to chicken wire. When he lost that job, Pownall signed on with Convair, which became General Dynamics. He came to Washington when General Dynamics won the contract to build the Atlas rocket in 1959. Four years later he moved to Martin Marietta, became head of the aerospace division in 1969, president in 1977, and CEO in 1982.

Four months later William Agee, then chairman of Bendix, began his bid to take over Martin Marietta. Pownall countered with his "Pac-Man defense," buying Bendix stock to counter Agee's purchase of Martin Marietta stock. The day Bendix backed down, a banner went up on the flagpole at Martin Marietta headquarters in Bethesda. It read, "Don't Tread on Me."

Martin Marietta grew and prospered under Pownall. Today its businesses include electronics, communications, information management, energy systems, and new materials, as well as aerospace and military systems.