The top tier of the cellblock — the level above the occupied cells — was largely unoccupied and rarely patrolled. It became a workshop.
The scale of what they constructed there is what distinguishes this escape from most. The men did not simply find a gap in the security and squeeze through it. They spent months building the equipment that would take them across the bay.
The life preservers were made from more than fifty prison-issue raincoats. The raincoats were acquired by donation and theft — some inmates who knew generally what was happening provided their coats voluntarily; others’ coats disappeared from the workshop or the coat storage without being directly connected to any single person. The rubber material of the raincoats was cut, stitched together by hand with improvised needles, and sealed with a liquid plastic compound. The result was inflatable flotation devices based on a design reportedly drawn from an article in the March 1962 issue of *Popular Mechanics*.
The raft itself was larger — approximately six by fourteen feet when inflated. The same raincoat rubber, the same hand-stitching, the same liquid plastic sealer. A *Sports Illustrated* article on channel buoys reportedly provided design ideas for the raft’s construction. The men had access to magazines in the prison library, and they used that access practically.
Paddles were fashioned from plywood. The workshop on the unused cellblock level was not visible from the main floor below, was not regularly searched, and apparently was not checked systematically during the months when the men were building their escape kit in it.