Figure 5. Biological growth on hydrolab after 
one year’s submergence off Florida coast near 
Palm Beach. Inspection of laboratory after 
removal of growth showed little corrosion had 
taken place. (West Palm Beach Post-Times 
photo) 
—Fluids for buoyancy and hydraulic systems, 
pressure compensating systems, and lubrication. 
Technology and knowledge of material per- 
formance in the ocean has not progressed to where 
final decisions can be made as to what materials 
and construction techniques are to be employed 
in future systems. Entirely new material concepts 
may be developed and employed by the year 
2000, but only if sufficient effort is expended in 
analysis, development, and use of a wide variety of 
materials. 
1. High Strength Steels 
a. Current Situation Ferrous materials having a 
yield strength of 80,000 psi (HY-80) or less have 
been used in all fleet submarines and in most deep 
submergence vehicles. HY-140 steels (130,000 to 
150,000 psi yield strength) now can be specified 
for use in noncombatant vehicles, although the use 
of HY-140 for combatant submarines awaits solu- 
tion to many problems in forging, fabricating, and 
welding large segments. 
Operations at 20,000 feet will require much 
stronger steels in excess of 180,000 psi yield 
VI-42 
strength or advanced nonferrous or nonmetallic 
materials. 
If many pressure cycles are involved, failure due 
to fatigue rather than crushing forces must be 
considered. Unfortunately, as yield strength in- 
creases, toughness and fatigue life decrease. Each 
time a vehicle descends to operating depth and 
returns, a fatigue cycle is incurred. If a collapse 
safety factor of 1.5 is incorporated, cyclic loading 
would vary from zero psi to a maximum of 86,500 
psi for HY-140. 
Data suggest that HY-80 can sustain 10 times 
the cyclic loading of HY-140; however, the 10,000 
cycle capability for HY-140 steel is likely to be at 
least three times the cycles a submersible will 
undergo during its useful life. Since HY-140 
fatigue life is ample, it is not correct to imply that 
an HY-140 vehicle will have a shorter service life 
than an HY-80 vehicle. This would be true only if 
service life extended beyond 60 years with dives to 
maximum depth every other day. 
b. Future Needs While steel has a higher density 
than other materials considered for pressure hulls, 
new ultra-strength steels (yield strength greater 
than 240,000 psi) may produce in 15 years 
efficient 20,000-foot pressure hulls (W/D around 
0.5) for small, maneuverable noncombatant ve- 
hicles. 
Although other materials may be used for 
vehicle and habitat structures, high strength steel 
may be found the least costly once stress corro- 
sion cracking and brittle failure problems are 
overcome, and manufacturing and fabrication 
techniques developed. 
Currently HY-80 steel, for which suitable man- 
ufacturing and fabrication techniques have been 
developed, is much less expensive than any other 
material proposed for pressure hulls. If ultra- 
strength steel technology were successful, a 20,000- 
foot hull with W/D ratio around 0.5 would be 
possible and steel might remain the most econom- 
ical material. 
2. Nonferrous Metals 
a. Current Situation Titanium and aluminum 
materials, much less dense than steel, show prom- 
ise for low W/D ratio hulls for deep submergence 
vehicles. However, fabrication technique and cor- 
rosion unknowns have limited such materials to 
