Summary of Submarine Collapse Event Information
By Bruce Rule - September 2, 2013
For future reference, hopefully never needed, this posting summarizes, in one document, what the writer knows about six events involving the hydrostatic collapse of submarine pressure-hull and internal bulkhead structures with reference to test-depth and calculated (predicted) collapse depths. This compilation includes one event not previously discussed for which specific details cannot be provided.
1. USS STERLET (SS-392) Collapse of the torpedo room bulkhead which triggered collapse of the torpedo room pressure-hull – or vice versa – at depth of 1200-feet. (The torpedo room was the only sealed compartment; all other areas were open to the sea during this controlled event.) Test-depth of main pressure hull: 400-feet: Torpedo room bulkhead and pressure-hull designed to survive to 1100-feet. Actual collapse: predicted depth plus nine percent (1200/1100). Energy release: equal to the explosion of 840 pounds of TNT at a depth of 1200-feet. The volume of the forward torpedo room was 4460 cubic feet, the collapse event bubble-pulse frequency was 9.2 Hz. The after escape trunk, with a volume of 88 cubic feet, collapsed at a depth of 9100-feet with an energy release of 84 pounds of TNT. The bubble-pulse frequency was 105-Hz. The forward escape trunk, with a volume of 43 cubic feet, collapsed at a depth of 10,300-feet with an energy release of 175 pounds of TNT. The bubble-pulse frequency was 91-Hz. ((Note: the USS CHOPPER (SS-342) survived a depth excursion to 1020-feet, bow-down at an 82-degree angle as determined from grease that ran down the galley bulkhead. Source: Don Forbes, then the CO. Chopper suffered severe structural damage and was decommissioned.))
2. Collapse of an internal bulkhead of a partially flooded pressure-hull at about 1400-feet which triggered collapse and fragmentation of the pressure-hull. Rated depth of the internal bulkhead not known. Energy release: equal to the explosion of about 2500 pounds of TNT at 1400-feet.
3. Collapse of the intact SCORPION pressure-hull at 1530 feet with a 50-foot telescoping of two after compartments. Bow section separated but intact. Screw and attached shaft fell separately from collapse depth. Test depth: 700-feet, predicted collapse depth: 1050-feet (test-depth plus 50%). Actual collapse: predicted depth plus 45 percent (1530/1050). Energy release: equal to 13,200 pounds of TNT at 1530-feet. The bubble-pulse frequency was 4.46 Hz. More than 17 collapse events occurred during the 200-second period that followed collapse of the pressure-hull. The source of these signals is assessed to have been structures that survived within the wreckage to collapse at depths as great as about 6000-feet. Based on the distribution of energy peaks below 400 Hz, six of these events are assessed tp have been the collapse of SCORPION torpedo tubes at depths between 3400 and 4600-feet. The absence of bubble-pulse acoustic energies from these follow-on collapse events is attributed to the same long-range propagation channel attenuation and distortion effects documented for the low-frequency spectra of the SUB-MISS calibration shots dropped near the wreck-site. Only the SCORPION pressure-hull collapse bubble-pulse signal had the energy level needed to “survive” these effects. This subject is more extensively discussed in WHY THE USS SCORPION (SSN-589) WAS LOST.
4. Collapse of the intact THRESHER pressure-hull at 2400-feet with fragmentation into six major sections; no telescoping. Test-depth: 1300-feet; predicted collapse depth: 1950-feet. Actual collapse: predicted depth plus 23 percent (2400/1950). Energy release: equal to 22,500 pounds of TNT at 2400-feet. No collapse events subsequent to collapse of the pressure-hull were acoustically detected, the assessed result of the greater energy release of the THRESHER pressure-hull collapse event relative to SCORPION: 70 percent greater; the event was almost 900 feet deeper and the pressure was about 390 psi greater: 1070 versus 680.
5. NOVEMBER Class Soviet SSN K-8. Collapse of the torpedo room bulkhead which triggered collapse of the torpedo room pressure-hull – or vice versa – at depth of 2020-feet. Maximum safe depth: 790-feet, never-exceed depth (test depth): 985 feet; predicted collapse depth: 1250-feet. Actual collapse: predicted plus 60 percent (2020/1250). Energy release: equal to 1050 pounds of TNT at 2020-feet. Bubble-pulse frequency: about 13-Hz.
6. MIKE Class Soviet SSN (titanium pressure-hull). Collapse of torpedo room bulkhead which triggered collapse of the torpedo room pressure hull or vice versa after 10 mins on the sea floor at a depth of 5530-feet. Maximum safe depth: 3350-feet; never-exceed depth (test-depth): 4100-feet; predicted collapse depth: 4900-feet. Actual collapse: predicted plus 13 percent (5530/4900).