Bob Croft’s 23 years in the US Navy encompassed 12 years on submarines and 10 years as a diver. NAUI and PADI certified, he has taught Navy SCUBA divers and is personally qualified in both deep sea air and deep sea mixed gas diving. He served on 6 subs, 2 small submersible’s, the X-1, a 4-man sub and as support crew for the bathyscaph Trieste II.
Croft is credited with inventing “air packing” (also known as “lung packing” or “glossopharyngeal inhalation”), a method used to overfill the lungs, increasing the volume of air in the lungs above the total lung capacity prior to breath-holding.
A navy research team, Dr Karl Schaefer (US Navy) and Dr Robert Allison of the Scott White clinic in Tempel Texas, had done research on diving mammals demonstrating that air-breathing animals could go to half a mile and deeper without experiencing thoracic squeeze. The discovery of the “blood shift” phenomenon opened a host of theories regarding free diving humans. Croft served as that research subject to determine if that same “blood shift” occurred in humans and measure it. This led to the published study on pulmonary and circulatory adjustments determining the limits of depths in breathhold diving. Science, 162(857), 1020-3.
His experience working 5 hours per day, 5 days a week at the 118-feet deep 250,000-gallon submarine escape training tank provided him an opportunity to salve his curiosity about holding his breath underwater. From an initial breath-hold time of 1½ to 2 minutes, after a year he was able to hold his breath for over 6 minutes, dropping to the bottom of the tank and sitting there for over three minutes and then returning to the surface at a relaxed pace. In 1967, at the encouragement of his fellow instructors, Croft participated in competitions over an 18 month period, establishing three depth records: 212 feet (64 m) in 1967; 217 feet (66 m) in 1968; 240 feet (73 m) in 1968. He retired from free-diving thereafter.
Bob Croft is no stranger to public speaking having appeared on the Today Show with Barbara Walters and Hugh Downs, and he has presented at various diving venues throughout the US and Canada, to audiences as large as 1,200. He was featured in a CBS documentary “Dive to the Unknown”, produced by Al Giddings.