they must return to the undersea job site. Decompression is carried out comfort-
ably and safely on the support ship.
The Navy developed four deep diving systems: ADS-IV, MK 1 MOD 0, MK 2
MOD 0, and MK 2 MOD 1.
ADS-IV. Several years prior to the Sealab I experiment, the Navy successfully de-
ployed the Advanced Diving System IV (ADS-IV) (see Figure 1-18). The ADS-IV
was a small deep diving system with a depth capability of 450 fsw. The ADS-IV
was later called the SDS-450.
MK 1 MOD 0. The MK 1 MOD 0 DDS was a small system intended to be used on
the new ATS-1 class salvage ships, and underwent operational evaluation in 1970.
The DDS consisted of a Personnel Transfer Capsule (PTC) (see Figure 1-19), a
life-support system, main control console and two deck decompression chambers
to handle two teams of two divers each. This system was also used to operationally
evaluate the MK 11 UBA, a semiclosed-circuit mixed-gas apparatus, for satura-
tion diving. The MK 1 MOD 0 DDS conducted an open-sea dive to 1,148 fsw in
1975. The MK 1 DDS was not installed on the ATS ships as originally planned,
but placed on a barge and assigned to Harbor Clearance Unit Two. The system
went out of service in 1977.
Figure 1-19. DDS MK 1 Personnel Transfer Capsule.
Figure 1-20. PTC Handling System, Elk
MK 2 MOD 0. The Sealab III experiment required a much larger and more capable
deep diving system than the MK 1 MOD 0. The MK 2 MOD 0 was constructed
and installed on the support ship Elk River (IX-501). With this system, divers
could be saturated in the deck chamber under close observation and then trans-
ported to the habitat for the stay at depth, or could cycle back and forth between
the deck chamber and the seafloor while working on the exterior of the habitat.
CHAPTER 1 -- History of Diving