This window is not trivial. It is long enough that a person who entered the water in a functional raft and paddled actively toward Angel Island — which the Delft study placed approximately 1.5 miles from the launch point, achievable in roughly 90 minutes of active paddling under moderate conditions — could potentially complete that crossing before hypothermia became incapacitating.
The critical variable is immersion versus raft occupancy. A person in a raft is not immersed. They are exposed to cold air and water spray, which causes some heat loss, but the rate of core temperature reduction is significantly slower than for a person fully immersed. If the raft held up and the men were paddling rather than swimming, the physiological clock ran more slowly than the FBI’s initial assessment — which appears to have been based on open-water swimming exposure — would suggest.
The men were also not young, sedentary, or physically compromised. Morris was 35. John Anglin was 32. Clarence Anglin was 31. They had been in Alcatraz for more than two years, working in a prison environment where manual labor was part of the institutional structure. They were not in the peak condition of trained athletes, but they were not in the condition of sedentary civilians whose exposure to physical demand had been minimal. The physiological tolerance for cold stress in physically active middle-aged men is higher than in the general population.
This does not prove survival. It identifies a physiological basis on which survival was possible within the window the Delft study suggested was hydrodynamically available. Physics and physiology together establish: under the right conditions, the crossing was survivable. Whether the conditions were right, on that specific night, is what the evidence cannot determine.