Berry L . Cannon Berry Louis Cannon ( March 22 , 1935 – February 17 , 1969 ) was an American aquanaut who served on the SEALAB II and III projects of the U . S . Navy . Cannon died of carbon dioxide poisoning while attempting to repair SEALAB III . It was later found that his diving rig ' s baralyme canister , which should have absorbed the carbon dioxide Cannon exhaled , was empty . Early life and education . Cannon grew up in Williston , Florida , where he was raised by his grandmother . He was captain of his high school football team . Cannon joined the United States Navy after high school and served for four years , becoming a mineman second class . He served at one time at the Hawthorne Naval Ammunition Depot in Hawthorne , Nevada , where he was on the boxing team . Cannon graduated from the University of Florida in 1962 with a degree in electronic engineering . SEALAB II . Cannon was a civilian electronics engineer at the U . S . Navy Mine Defense Laboratory in Panama City , Florida , where he designed intercommunications systems . From August 28 to September 12 , 1965 , Cannon served on the first crew of SEALAB II near La Jolla , California . He received the Navy ' s Superior Civilian Service Award for his participation in the project . SEALAB III . In 1969 , Cannon was assigned to Team One for the SEALAB III project , which would take place off San Clemente Island . He was one of four members of Team One assigned to open and secure the habitat , alongside fellow aquanauts Robert A . Barth , Richard Blackburn and John Reaves . On February 16 , 1969 , the SEALAB III habitat sprang a leak . Cannon , Barth , Blackburn and Reaves were twice sent down to SEALAB in the Personnel Transfer Capsule ( PTC ) in an attempt to repair the problem . Shortly after 0500 hours on February 17 , Cannon began to convulse while working on the exterior of the habitat . Barth tried to save him , holding his head in the breathable gas pocket of the skirt surrounding SEALAB ' s entrance and unsuccessfully attempting to force the mouthpiece of the emergency aqua - lung regulator between Cannon ' s teeth . Finally , Barth dragged Cannon back toward the PTC , where his fellow aquanauts helped him bring Cannon inside and Reaves and Blackburn attempted resuscitation . When the PTC reached the surface it was obvious that Cannon was dead . His body was placed in the outer airlock of the deck decompression chamber ( DDC ) , returned to surface pressure and brought to San Diego Naval Hospital . Cannon ' s funeral was held at Humphrey Mortuary in Chula Vista , California , on February 19 . He was buried at Wacahoota Baptist Cemetery in central Florida . Aftermath . It was widely reported in the news media that Cannon had died of a heart attack . However , the official board of inquiry , held in San Diego from February 28 to March 12 , 1969 , concluded that Cannon had in fact died of carbon dioxide poisoning . The carbon dioxide - scrubbing baralyme canister on Cannon ' s Mark IX diving rig was empty . The SEALAB III aquanauts , including Cannon , did not set up their own diving rigs . The identity of the person who failed to refill the baralyme canister was never determined . SEALAB medical officer Paul G . Linweaver later suggested that Cannon would have realized his equipment was faulty had he not been suffering from extreme cold due to breathing pressurized helium . Surgeon commander John Rawlins , a Royal Navy medical officer assigned to the project , also suggested that hypothermia was a contributing factor . According to John Piña Craven , the U . S . Navy ' s head of the Deep Submergence Systems Project of which SEALAB was a part , SEALAB III had been " plagued with strange failures at the very start of operations " . According to Craven , while the other divers were undergoing the weeklong decompression , repeated attempts were made to sabotage their air supply by someone aboard the command barge . Eventually , a guard was posted on the decompression chamber and the men were recovered safely . A potentially unstable suspect was identified by the staff psychiatrist but the culprit was never prosecuted . Craven suggests this may have been done to spare the Navy bad press so soon after the USS " Pueblo " incident . As a result , it has been suggested that Cannon ' s death was a murder . Personal life . Cannon was married to Mary Lou Cannon and had three sons . He was known for seldom complaining if his complaint would go against command authority . He enjoyed reading the works of Zane Grey .