INTRODUCTION 
The development of deep diving vehicles which can stay submerged 
for long periods of time has focused attention on the deep ocean as an 
operating environment. This has created a need for information con- 
cerning the behavior of common materials of construction as well as 
newly developed materials with promising potentials at depths as well 
as at the surface in seawater. 
Since 1959 the Naval Civil Engineering Laboratory has been develop- 
ing the technology necessary for designing, constructing, inspecting 
and maintaining structures and fixed equipment on the ocean floor. A 
part of this program is to determine the effects of deep ocean environ- 
ments on the corrosion of metals and alloys. 
In order to determine the effects of deep ocean environments on 
the corrosion of metals and alloys, a Submersible Test Unit (STU) was 
designed to which many test specimens can be attached. A STU unit is 
shown in the inset of Figure l. 
The test sites for the deep ocean exposures are shown in Figure 1 
and their specific geographical locations are given in Table 1. The 
complete oceanographic data at these sites, obtained from NCEL cruises 
between 1961 and 1967, are summarized in Figure 2. Initially it was 
decided to utilize the site at the 6,000-foot depth (STU I-1, 2, 3 and 
4). Because of the minimum oxygen concentration zone found between 
the 2,000- and 3,000-foot depths during the early oceanographic cruises, 
it was decided to establish a second site (STU II-1 and 2) at a nominal 
depth of 2,500 feet. For comparative purposes the surface seawater 
Site V was established. Even though the actual depths are shown in 
the tables, the nominal depths of 6,000 and 2,500 feet are used through- 
out the text. 
A summary of the characteristics of the seawater 10 feet above the 
bottom sediments at the two deep ocean exposure sites and 5 feet below 
the surface at the surface exposure site is given in Table l. 
Sources of information pertaining to the biological characteristics 
of the bottom sediments, biological deterioration of materials, detailed 
oceanographic data, and construction, emplacement and retrieval of STU 
structures are given in Reference 1. Bottom sediments, as used herein, 
means the water-mud interface to a mud depth of about 6 inches. 
The procedure for the preparation of the specimens for exposure and 
for evaluating them after exposure are described in Reference 2. 
Previous reports pertaining to the performance of materials in the 
surface and deep ocean environments are given in References 1 through 
12, 
