because of the very high compressive strength of glass, which also becomes 

 more impact resistant as it is stressed during submergence in the ocean. This 

 concept was supported by analytical calculations and exploratory experiments 

 with small-scale glass spheres. Although this concept extends the depth range 

 considerably beyond Piccard's and imposes extremely high-stress loading on 

 the capsule material (glass), it has been favorably received. Since 1963 explor- 

 atory research has been conducted by the Navy to develop Perry's concept 

 into operational hardware. 



Piccard's and Perry's concepts were specifically oriented to depths 

 beyond the continental shelf, and only to submarines or bathyscaphs. Neither 

 of these two concepts answered the growing need for the exploration and 

 utilization of the continental shelf by means of divers supported by specialized 

 mechanical systems operated by nondivers enclosed in 1-atmosphere, pressure- 

 resistant capsules (Figure 1). To fill this gap, Navy scientists and engineers of 

 the Naval Missile Center (NMC), Point Mugu, and the Naval Civil Engineering 

 Laboratory (NCEL) 3 proposed research that would result in a transparent 

 capsule for manned operations at continental shelf depth within the shortest 

 possible time. Immediate practical application of the transparent capsule 

 concept would consist of developing a 66-inch man-size capsule and mating 

 it with life-support and winch-down subsystems resulting in a bottom tethered 

 manned observatory with vertical water column mobility (Figure 2). Besides 

 serving as the focal point for the acrylic plastic capsule project, NEMO (Naval 

 Experimental Manned Observatory)* was to be utilized by NCEL engineers as 

 an in-situ underwater control center to supervise and counsel Seabee diver 

 teams performing ocean engineering construction experiments on the conti- 

 nental shelf floor, while NMC scientists were to use NEMO as an in-situ 

 observatory for the scuba diver and porpoise performance studies. 



Since the overriding requirement for NEMO was that it become 

 operational within the shortest span of time, past concepts for transparent 

 capsules were reviewed with this requirement in mind. Perry's concept for 

 a glass capsule was rejected because at that time there were no molds in this 

 country capable of reliably producing large glass hemispheres, and it appeared 

 that funding in excess of available exploratory funds would be required to 

 design and purchase such molds, develop the casting process, and test a suffi- 

 cient number of such capsules to establish confidence limits for their 

 performance. Instead, Piccard's concept employing spherical acrylic plastic 

 pentagons was chosen. 



* Earlier designated Naval Edreobenthic Manned Observatory. 



