I-400 Class Submarine
Dive site
The I-400 class submarines were the largest submarines built before the nuclear age — each designed to carry three folding Seiran floatplanes for attacks on the Panama Canal. One of these extraordinary vessels rests in Bikini's lagoon at 55 meters, its 120-meter hull essentially intact. The aircraft hangar forward of the conning tower is identifiable and the floatplane launch catapult remains in position. This is technical diving territory given the depth, but the historical significance is unmatched: these boats represented the peak of Imperial Japanese submarine engineering and their existence was kept secret from the Allies until the war's final weeks.
Conditions
Depth
40 to 55 m
Advanced depths
Current
Usually gentle
Can pick up on the edge
Visibility
20 to 35 m
Clearest in the calm season
Water
27 to 30°C
3mm wetsuit
Month by month
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Water (°C) | 27 | 27 | 28 | 28 | 28 | 27 | 27 | 27 | 27 | 27 | 27 | 27 |
| Vis (m) | 20 | 22 | 25 | 25 | 22 | 20 | 18 | 18 | 18 | 18 | 20 | 20 |
| Current | Gentle | Gentle | calm | calm | calm | Gentle | Moderate | Moderate | Moderate | Gentle | Gentle | Gentle |
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