6-56 Change A
U.S. Navy Diving Manual—Volume 2
MK 21 MOD 1 General
Characteristics
Principle of Operation:
Surface-supplied, open-circuit system
Minimum Equipment:
1.
MK 21 MOD 1 Helmet
2.
Harness
3.
Weight belt (if required)
4.
Dive knife
5.
Swim fins or boots
6.
Surface umbilical
7.
EGS bottle deeper than 60 fsw
Principal Applications:
1.
Search
2.
Salvage
3.
Inspection
4.
Underwater Ships Husbandry and enclosed
space diving
Advantages:
1.
Unlimited by air supply
2.
Head protection
3.
Good horizontal mobility
4.
Voice and/or line pull signal capabilities
5.
Fast deployment
Disadvantages:
1.
Limited mobility
Restrictions:
1.
Work limits: 190 fsw
2.
Emergency air supply (EGS) required deeper
than 60 fsw or diving inside a wreck or
enclosed space
3.
Current - Above 1.5 knots requires extra
weights
4.
Enclosed space diving requires an Emergency
Gas Supply (EGS) with 50 to 150 foot whip
and second stage regulator.
Operational Considerations:
1.
Adequate air supply system required
2.
Standby diver required
Figure 6-25. MK 21 MOD 1 General Characteristics.
MK 21 MOD 1 Helmet.
