Snorkel in the US Navy - 1945 onwards
This article makes no claim to any direct knowledge of the systems of the US Navy, the author having served in the Submarine Branch of the Royal Navy in the early days of snorting. What follows is brief description of the US Navy snorkel conversion garnered from the documents listed below and is intended to be complementary to the article Snorting in the Royal Navy - 1945 Onward and as an adjunct to the article US Navy Guppy Submarine Conversions 1947-1954
The primary sources are a detailed description of the Engine Induction and Exhaust system of the Fleet Submarine prior to the fitting of snorkel system in Chapter 7, Ventilation System, 'THE FLEET TYPE SUBMARINE' June 1946 NavPers 16160, and 'THE SUBMARINE', part 15, The Snorkel System, revised 1955, NavPers 16160-A'. Both being training manuals of the US Navy. The copy of the latter document was kindly provided by Keith Allen of the USA.
Attached as appendices is a complete description of the US Navy Fleet Submarine snorkel system and operation made available by Bob Emery of the Submariners Association of Canada West. The Royal Canadian Navy had at one time operated two former US Navy Fleet Submarines.
In this article I have focused on snorting the US Navy, however there is a complimentary article Snorting in the Royal Navy - 1945 Onward
The first US Navy submarine placed in operational service with snorkel was the USS Irex (SS 328) in 1947, a Fleet Submarine of the Tench class originally completed in 1945.
See Appendix A for details of the history of US Navy snorkel development leading up to the conversion of the USS Irex.
This successful conversion design was applied to the parallel Guppy conversion program, the first conversion completed in 1947.
Later when the Guppy conversions proved too expensive, a program was initiated to add snorkel to 18 Fleet Submarines of the similar Balao and Tench classes. In general apart from snorkel, they remained as first built but to accommodate the snorkel masts, the older style conning towers were converted to a stepped fin as seen in the early Guppy conversions. This class of 18 submarines were known as Fleet Snorkels. The fitting of snorkel usually took place as part of regular shipyard overhauls.
It should be noted that apart from the more formal program of 18 submarines, others were also fitted with snorkel throughout the US Navy Submarine Fleet.
All Fleet Submarines conversions of any type were progressively phased out as the US Navy Submarine Service moved to become entirely nuclear propelled. A significant number were handed over for service with foreign navies.
This information was taken from THE FLEET SUBMARINE IN THE U.S. NAVY by Commander John D Alden. US Navy (ret).
Extract from Admiral Galantin's SUBMARINE ADMIRAL Page 136
USS Pickerel (SS 524) was one of the Guppy GII. Under her innovative, daring skipper, Commander Paul R Schratz, she demonstrated the ultimate performance of the snorkel. She was the first Guppy to be deployed to the Far East, and in returning to Pearl Harbour from Hong Kong she snorkelled all the way, 5194 miles in 505 hours. It required careful planning, superb engine operation and maintenance, and great physical stamina and determination. Her twenty-one days continuously submerged in 1950 remained a record until 1958, when nuclear powered Seawolf made her sixty day test.
Note. Presumably the Admiral means a record for the US Navy as HMS Alliance was submerged for 30 days continuously during her snort cruise in 1947. However she only covered 3193 miles. The Pickerel apparently achieving the remarkable average submerged snorkel speed of 10.28 knots per day.
While the detail in Appendix F Item 1 appears to repeat much of what has been stated in Appendix B, Appendix C, Appendix D and Appendix F about the Fleet Submarine conversions, it should be appreciated the US Navy submarine veteran who contributed this anecdote is describing the snorkel system on the new diesel submarine Blueback, one of three Barbel class constructed for US Navy after the war, with snorkel integrated into the design.
The Barbel class were the only US Navy diesel submarines with the revolutionary hull shaped developed in the trial submarine USS Albacore (AGSS 569), launched in 1952. Incidentally this shape became the basis of the hulls of US Navy SSN submarines starting with the Skipjack class of 1958. The USS Barbel (USS 580) was commission in 1959, more than a decade after the first snorkel submarine, USS Irex (USS 482), 1947, yet in principle little had changed.
It is of interest that he confirms other sources that suggest that the Barbel class had a similar snorkel system to that of the much earlier post war Tang class.
The lead submarine, USS Tang (SS 563) was launched in 1951, and from these dates we can speculate that the both the snorkel systems for the conversions and the new submarines were being developed at the same time. The only significant difference appears to have been the use of a dry induction mast in the new submarines that also only had one engine room. There the US Navy diesel snorkel story stops.
A full description of development and application will be found in these attached documents.
- Appendix A Submarine Snorkel System Development in the US Navy.
- Appendix B Air Induction & Snorkel Induction Systems.
- Appendix C Snorkel Exhaust System.
- Appendix D Snorkel Electrical & Engine Safety Circuit Systems.
- Appendix E Fleet Submarine Snorkel Operating Procedure.
- Appendix F Anecdotes.
- Appendix G U-Boat History, Development & Equipment, 1914 to 1945 by David Miller.
A SUMMARY OF THE CONVERSION
Before proceeding it should made clear that all the main piping is outside the pressure hull under the outer shell. In the simple diagrams mentioned below, equipment within the pressure hull is so indicated.
Basically the systems used in the US Navy Fleet Submarines were similar to those described in the companion article Snorting in the Royal Navy - 1945 Onward . That is a single air induction mast and a single exhaust mast, but all rather more complicated in application.
There were two engine rooms each with two diesel-generators. These big submarines were not direct drive, with at all times the screws being driven by electric motors supplied from the batteries alone when submerged and the diesel-generators when surfaced. The four diesel-generators could be arranged for 'all propulsion' for maximum surface speed (19 knots) or both propulsion and charging the batteries.
Various sources suggest that this propulsion arrangement was more suitable or snorkelling than direct drive, in that no forward way was lost when snorkelling was shut down due to a temporary loss of trim, the battery continuing to supply the motors without any break in supply.
This propulsion arrangement also brought about a rather different crew organisation for snorkelling than the early Royal Navy direct drive, where the engines were directly propelling the submarine, see Appendix E. In the post war scene, the Royal Navy adopted this method of 'all-electric' propulsion in the converted T Class and the Parthian Class & Oberon Class. The later Royal Navy Upholder Class, like all modern multi-engine single screw submarines, had the single screw driven exclusively by one large electric motor.
There has been a suggestion that the four stroke Royal Navy engines were more tolerant of being occasionally flooded through the open exhaust than the US Navy two stroke. Appendix F Anecdote 4 gives a clue about this aspect of snorkelling. It is known the US Navy engine piston heads were modified for snorkel.
On the surface the main engine air inlet was through a 36 inch ventilation stack and valve (also described as the main induction valve) in a compartment in the lower after part of the bridge, open to the sea when dived.
The stack was mounted on the outside of the pressure hull, raised by mounting legs.
The stack distributed air to the two engine rooms and ships ventilation through 22 inch pipes installed on the outside of the pressure hull.
The output air of the piping was admitted through the pressure hull into each engine room by a manually operated induction hull valve. A detailed drawing of this hull valve is shown in Appendix B.
Also connected to the 36 inch ventilation stack was an additional outlet pipe feeding the aft air inlet for the ventilation system with a similar but smaller hull valve.
To recap, on the surface air was taken in through the bridge structure and fed into each to the two engine room compartments, with additional air fed into the vessel for ventilation. Each point of entry into the pressure hull could be sealed for diving by an adjacent hand operated valve. A simple line diagram has been provided to assist the reader of this section of the summary,
Pre Snorkel Exhaust
Each engine had inboard and outboard exhaust valves, in much the same arrangement as the Royal Navy. However the individual outboard valves to each of the four surface mufflers were hydraulically operated.
It is interesting to note that the inboard valve appears to be a sluice type as fitted in 1968 to Royal Canadian Navy 'O' class.
Both inboard and outboard exhaust valves were water cooled, the inboard by water from the engine fresh water system, the outboard by water from the engine salt water system.
So to recap, the original engine exhaust set-up was quite straightforward with each of the four engines having separate valves and mufflers.
Snorkel Induction Conversion
The conversion to snorkel involved the replacement of the former conning tower structure with a modern style stepped 'Sail' supporting the periscopes and the various masts including the telescopic snorkel induction mast and the single telescopic snorkel exhaust mast.
The induction air from the snorkel mast was taken through a large water separator and a hydraulically operated shut off induction valve to a new inlet in the structure of the 36 inch ventilation stack still in its former position but now enclosed by the after part of the sail as shown inset in Fig 1.
The distribution of air from the 36 inch ventilation stack remained as before apart from a change in the ship's ventilation system that appears to have been simplified.
Previously there had been a partial bye-pass from 22 inch pipe feeding the main induction to the aft engine room. This bye-pass supplied air to the single ventilation hull valve aft in the manoeuvring room, while the 16 inch pipe from the 36 inch ventilation stack fed a ventilation hull valve in the forward engine room. Hence there were two smaller type ventilation hull valves.
In the snort conversion the hull valve in the forward engine room and the partial bye-pass were apparently removed. The ship's 16 inch ventilation pipe then simply ran from the 36 inch ventilation stack to the existing ventilation hull valve aft. No text explanation of this aspect of the conversion is available but this is the arrangement shown in all the drawings associated with this article and appendices. Also there is nothing in the text to indicate major changes in the battery ventilation as was the case with the Guppy conversions.
Snorkel Exhaust Conversion
Turning to the engine exhaust, obviously the previously four quite separate engine exhaust systems had to be joined together to form a single pipe to the snorkel exhaust mast.
It was also considered desirable to isolate the piping etc, of the unused engines from that of the snorkelling engines. The result was a relatively complicated set of valves and piping. A complete description is provided in Appendix C, but a simple line diagram has been provided to assist the reader.
It should be noted most of the exhaust piping is pressure tight and not flooded at any time. Check drains were fitted.
Induction Mast Head Valve
The induction mast had a head valve that closed to prevent the ingress of sea water if the submarine lost trim and went below snorkel depth. Unlike the British who developed their own version of the widely used U-Boat float operated valve, the US Navy adopted a design where the head valve was opened and closed by high pressure air, controlled by electrically operated valves.
Appendix A suggests this alternative to the U-Boat float valve, was another German development and this is confirmed by Appendix G. Though this reference also states the development was not completed before WWII ended.
It is quite clear from a photograph of the snorkel head valve from U-3503, that float valves were being used on at least one of the latest German type XXI submarines of WWII. The scuttled U-3503 was raised by the Swedish Navy and dismantled. More photographs can be seen here
It is reasonable to assume that the Type XXI U-Boats put into trials service by the US Navy had similar float valves, but that the US Navy chose to proceed and complete the development of the German electro-pneumatic snorkel head valve and this became standard in the US Navy.
The Icelandic owned website UBoat.net that extensively records the history of the German U-boat Service, shows a post WWII drawing of three different U-Boat snorkel head valves with little background text. Included are the float and the electro-pneumatic versions. No original German source is given for these drawings.
Regardless of the origin of the design, the US Navy exclusively used an electro-pneumatic electrical head valve control system automatically operated by salt water sensitive electrodes mounted on the snort head.
Thus if the electrodes were flooded, the head valve was closed. The closing of the head valve was assisted by springs and should the air pressure fail the springs would close the head valve. When the electrodes were clear of sea water, the head valve would again be opened by HP air.
Unlike Royal Navy conversions with a simple open outlet to the sea , the US Navy snorkel exhaust mast had a fairly complex diffuser head that added a venturi-like action to aid in the exhaust process. It was of course still open to mast flooding if the engine back pressure dropped too much.
The exhaust mast raising mechanism was driven by the same hydraulic motor that raised the induction mast, but the gearing was such that the required relative difference in heights when raised was achieved by using a different gear ratio for each mast, hence the induction mast and exhaust masts were raised as one unit, described in Appendix C. and the relative heights can be seen in the photographs below. This arrangement has similarities to the German Type XXI U-Boat in that both masts were raised by the same mechanism, but in the XXI the two tubes were joined at the top with the inlets and outlets quite close together however further discussion of the Type XXI is beyond the scope of this article.
The main Snorkel Exhaust Valve (Able) was quite sophisticated in its operation. When the hydraulic pressure was applied to open the valve, it would not open until assisted by the increasing engine back pressure. The valve was designed to shut hydraulically against the engine exhaust pressure should the mast flood.
It should be noted that unlike Royal Navy submarines, there were automatic engine shut down facilities triggered by low vacuum, low engine back pressure and low engine rpm. Appendix F Anecdote No. 1, gives detail of the later Barbel class system that was basically similar to the original Fleet Boat conversion
Note: It is understood from various US Navy SubVet sources that only one engine room (two D/G) was used for snorkelling, usually the two forward D/G. However in the Guppy GIIA conversions, one diesel-generator was removed to make equipment space, detail of the lay-out and operation is not known.
Provided by Bob Emery of Submariner's Association of Canada West.
The 1955 US Navy training document includes a reference to the post-war submarines with snorkel fitted as part of the overall design, as ATTACK SUBMARINES. They were in fact the twin screw Tang class, the last numerically significant diesel class in the US Navy built in post WWII. The Parthian Class & Oberon Class of the Royal Navy submarines may reasonably said to be comparable. Both classes being the product of the early post-war thinking of both navies. There is some discussion in the Guppy conversions article.
One of the key changes was that unlike the US Navy conversions and British practice, the snorkel induction mast remained dry, that is not flooded when not in use. The induction mast head valve was apparently capable of keeping the mast watertight at any operating depth.
One drawing shows the induction being formed by two smaller pipes rather that one single but larger tube.
It is assumed the main reason for this dry mast was that it avoided dealing with 8000 lbs of sea water that in the conversions had to be either flooded into the induction mast when not in use or drained into the submarine when preparing snorkel. All these actions effect the management of the trim of the boat. Presumably the lesser amount of water in the exhaust mast of about 3000 lbs, was tolerable. One can speculate that this dry snort mast allowed a faster transit from snorkelling to a safe depth if in danger of attack.
Another significant change was the use of the snorkel induction mast head valve as the engine induction when running on the surface. This induction method seems to have been the pattern for most new post war submarines.
If the snorkel induction mast was still extended at 185 feet, it was automatically pressed down to the lowered position.
Much the same systems appear to have been used in the advanced class of three submarines, the Barbel class of 1959. As previously mentioned, there is quite a lot of detail in Appendix F Anecdote No. 1