NAVY DEPARTMENT
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                                      INDEX
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 After group of oil tanks:         Page | Engine room:                      Page
   Set valves to blow ...........    22 |   Valves closed ................    12
   Equalize pressure ............    37 |   Salvage hatch ................    37
   Blow dry .....................    37 |   Blown dry ....................    39
 Aground on Man-of-War Rock ..... 72-81 |   Main air induction valve ..... 14,31
 Ballast tanks:                         | Final salvage operations ....... 54-56
   Blowing ...................... 35,41 |   Vestal repairs pontoons ......    54
   Torch used on ................    35 |   Three pairs pontoons lowered
                                        |      and leveled ............... 54-56
   Break suction with ...........    37 |   Lashing started ..............    56
 Bureau of Construction and Repair      |   Preparations to blowing ...... 56-59
   undertook salvage ............     2 | Final blowing:
 Buoyancy:                              |   C.O.C. lost .................. 58,59
   Tables (preliminary) .........     6 |   Stern on surface ............. 59,60
   Reserve required .............     6 |   Bow and stern up .............    60
   Table of .....................    41 | Forward group of oil tanks:
   Table of (June 22, 1926) .....    44 |   Set valves and blow ..........    22
   Table of final available .....    58 |   Valves set for final blowing .    37
 Bow rose unexpectedly,                 | Lashing to prevent pontoons
   conditions when .............. 45-52 |   slipping ..................... 42,43
 Collision with City of Rome ....   1,2 | Leveling pontoons:
   Operating condition of S-51 ..     1 |   Reasons for ..................    39
   Condition after ..............     1 |   Difficulties met ............. 39,40
   First dive and procedure to locate 1 |   Method of .................... 40,41
   Derrick operations ...........   1,2 |   Risks taken .................. 40,41
 Conclusion ..................... 83-97 |   Experience ................... 44,56
 Control room:                          | Lifting stern first, reason for      7
   Start work on ................    14 | Lowering pontoons:
   Close ........................    20 |   First experience .............    22
   Use ship's air ...............    20 |   Negative buoyancy required ... 22,23
   Open Kingston valves .........    20 |   Result of calculations .......    24
   Close after door .............    20 |   Size of manila hawser required    24
   Ventilation valve ............    22 |   Experience ................... 24,25
                                        |   Effect of box keel ........... 27,28
 Cement:                                |   Final method of ..............    28
   Mixture used .................    33 | Maximum safe salvage angle .....     8
   Forced through 1.25-inch hose  33,35 | Mooring:
   Vent valve sealed ............    35 |   Anchors, chains, etc .........    10
 Divers:                                |   Method of .................... 10,12
   Available ....................  9,10 | Motor room:
   Training required for ........    10 |   Start of work on ............. 16,18
   Use of shallow water .........    16 |   Defects ...................... 16,29
   Enter battery room ...........    20 |   Leaks stopped ................ 29,31
   Pressure test on shallow water    23 | Pontoons:
   Diving class formed .......... 23,24 |   Strength, structure, weight of     9
   Maximum number down ..........    27 |   Delivered by derrick
                                        |      United States .............    25
   Interesting experience .......    42 |   Air leakage from .............    43
                                        |   Danger of air leaks ..........    44
 Diving:                                | Pumps, salvage .................     8
   Start of fall operations .....    12 | Salvage organization ...........     2
   Clearing way for .............    12 | Salvage hatch:
   Descending lines for .........    12 |   Conning tower ................    18
   Air hoses freeze .............    23 |   Handling .....................    20
   Discontinued for winter ......    23 |   Gun access ................... 18,20
   Start of spring operations ...    24 |   Engine room ..................    37
 Dry-dock operations ............ 81-86 | Spring operations, start of ....    24

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                                      INDEX

                                   Page | Towing:                           Page
 Suction effect ............ 7,37,41,50 |   Pennants and bridles for .....    44
 Torch, underwater, development and     |   S-51 under way to New York ... 60-72
   practice use of .. 23,24,25,39,42,52 |
 Tunnel:                                | Ventilation valves and piping .. 12,14
   First experience on .......... 14,16 |   Motor room ...................    29
   Recommenced and finished             |   Difficulties with ............    31
      first tunnel .............. 25,27 |   Cementing valves ............. 31,33
   Started second ...............    35 |
   New balanced nozzle used .....    35 | Weight, S-51 under water .......     4

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                            LIST OF PLATES AND FIGURES
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                                                                     Facing page
 Plate  1. Plan and elevation - Compartments, salvage, hoses, etc .......... 104
        2. Ventilation - Piping and valves ................................. 104
        3. Method of lowering pontoons from deck of Falcon ................. 104
        4. Method of leveling pontoons from deck of Falcon ................. 104
        5. Pontoon arrangement and salvage positions of S-51 ............... 104
        6. S-51 afloat on pontoons.  Plan view and sections showing actual
           arrangement of pontoons, July 5,1926 ............................ 104
        7. Record of diving days ........................................... 104
        8. Salvage pontoon - Structural plan ............................... 104
        9. Salvage pontoon - Arrangement ................................... 104
       10. Conversion of a mine sweeper to a salvage and submarine rescue
           vessel (U.S.S. Falcon) .......................................... 104

                                                                            Page
 Figure 1. Derricks attempting to raise stern. (Note slings) ...............   3
        2. Derricks attempting to raise stern. (Note maximum lift available)   5
        3. Divers on fall operations .......................................  11
        4. Iuka holding Falcon in position over wreck ......................  13
        5. Main induction valve bonnet. (Note 1-inch steel pipe which was
           jammed under valve disk) ........................................  15
        6. Channel strong back securing motor room hatch ...................  17
        7. Engine room salvage hatch.  Practice on S-50. (Note 4-inch hose)   19
        8. Gun access salvage hatch in position. (Note air connections) ....  21
        9. Bow pontoons. (Note nickel steel toggle bar through link, locked
           in position by 0.5-inch bolt each side) .........................  26
       10. Section of 12-inch air supply line to motor room, removed by divers30
       11. Twelve-inch supply pipe to motor room sealed by cover plate
           installed by divers .............................................. 32
       12. Superstructure deck removed by divers in way of main air induction
           valve. (Note strong back on this valve) .......................... 34
       13. Waldren's special balanced hose nozzle ........................... 36
       14. Engine room salvage hatch in position. (Note three air connections)38
       15. Stern pontoons which broke free from submarine, June 22, 1926 .... 47
       16. Bow pontoons driven out of alignment by the sea, June 22, 1926 ... 49
       17. Wickwire boarding bow pontoons, June 22, 1926 .................... 51
       18. Wickwire clearing air hose, June 22, 1926 ........................ 53
       19. Damaged pontoons aboard derrick United States at Point Judith .... 55
       20. Stern pontoons breaking surface. (Note action of air from pontoons)61
       21. Stern pontoons breaking surface. (Note action of air from pontoons)62
       22. S-50 supplying air to Falcon.  S-3 maneuvering alongside S-50.
           (Note 2.5-inch fire hose which carried air to Falcon) ............ 63
       23. Bow pontoons breaking surface .................................... 65
       24. Preparing tow to New York.  Sagamore in position ahead of S-51
           with Iuka at her bow ............................................. 66
       25. Tow under way - Vestal leading ................................... 67
       26. Arrangement of pontoons .......................................... 68
       27. S-51 afloat on pontoons.  (Note top of periscope shears and
           angle of heel) ................................................... 69
       28. Tow approaching Hell Gate.  Iuka alongside Sagamore .............. 71
       29. At the instant of grounding on Man-of-War Rock. (Note No. 2 pair
           of pontoons rising and drifting to starboard) .................... 73
       30. S-51 on Man-of-War Rock.  Clearing hoses in preparation of
           lowering pontoons ................................................ 74
       31. Twenty-five-ton derrick taking maximum strain on chains of port
           pontoon.  Pontoon below surface and diving boat in position for
           inspection of bottom ............................................. 76
       32. Bow pontoons below the surface at Man-of-War Rock.  Crew opening
           valves ........................................................... 80
       33. Falcon preparing to pass air hoses to top of stern pontoons.  S-51
           about to enter dry dock .......................................... 82
       34. S-51 entering dry dock ........................................... 84
       35. S-51 in dry dock. (Note arrangement of pontoons) ................. 85

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                            LIST OF PLATES AND FIGURES
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                                                                            Page
 Figure 36. S-51 on blocks.  Deck about 1 foot above water .................  87
        37. S-51 in dry dock.  Dock pumped down and bilge shores in place ..  88
        38. Divers who salvaged S-51 .......................................  89
        39. Detail view of gash resulting from collision with City of Rome .  90
        40. Port side view showing wrinkle caused by bow striking bottom
            after collision with City of Rome ..............................  91
        41. View showing damage to bow caused by grounding on Man-of-War Rock 92
        42. S-51 bow plating and stem casting on board Sagamore ............  93
        43. View of bridge badly bent to port from leaning against
            starboard No. 3 pontoon ........................................  94
        44. Damage to bilge keel and main keel due to grounding on
            Man-of-War Rock.  Note pieces of stone on bilge keel ...........  95
        45. S-51 afloat on her own buoyancy ................................  96

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                                    APPENDIXES
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 Appendix A. Diving crews on the S-51 ......................................  98
          B. Proposed layout of submarine rescue vessels ...................  99
          C. Diving operations in connection with salvage of the S-51.
             (From report of Lieutenant Hartley, commanding officer,
             U.S.S. Falcon) ............................................ 100-103
          D. Modifications to salvage pontoons ............................. 104