Submarine Diesels: Past, Present & Future

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Diesel submarines PAST

. From the early days of submarines to advanced fleet boats of World
War II, propulsion was a major factor affecting the use and tactics of submarines.

The first submarines in the early 1900's were initially used as a coastal defense platfom for breaking
suface ship blockades and patrolling coastal waters. U.S. submarines began with dangerous
gasoline engines. The U.S. Navy began testing diesels in submarines aound 1910. At first, thet proved unacceptable because the engines required rebuilding after 500 miles.  G4 was the last gasoline powered submarine. By 1915 the Navy moved to diesei power for safety and higher power output. A lack
of reliability and the inability to provide the required speed or range plagued diesel development.
The diesel engine was a key development in transforming submarines from defensive to
offensive units, providing the submarine with the speed and range necessary to attack ships far
from home port or supporting bases. Electric Boat designed submarines O-1 thru O-10 had the first satisfactory diesel engines. [see picture below]

When the war in the Pacific started, the newly developed
diesel-electric drive submarines provided what skippers needed to confidently conduct wartime
patrols. World War II submarines sank merchants and troop transports, an important task since
Japan relied heavily on imports of raw materials to support its war effort.
were initially conceived as coastal defense weapons. The Confederate Navy

used the hand powered Hunley to sink the blockading USS Housatonic in 1864. While the
Housatonic sank, so did the Hunley. The cost and risk associated with the submarine
outweighed possible benefits and they were not used again in attempts to break the Union
blockade.  Propulsion was one of the major failings of the early submarines. As new
technologies developed, the battery and internal combustion engine, submarines became popular.
The French envisioned using submarines to break blockades in 1886.They employed their
  battery powered submarine Gustav Zede in a successful mock attack against their battleship
Charles Martel in the first successful demonstration of a submarine as a weapon in 1901? Other ·
European countries quickly saw the importance of submarines as an effective weapon, but many
still believed that more development was necessary to make these early submarines truly
effective. Sir John Fisher, the First Sea Lord in 1904, believed the submarine needed greater
endurance to be used as an offensive weapon.  Endurance is the time a vessel can remain at sea
as opposed to range, which is the distance a vessel can travel. Both increased range and
endurance required larger submarines and countries struggled to build engines powerful enough
to drive them. Germany, which would become the builder of the most advanced and powerful
submarines by the end of World War I, did not believe submarines could be utilized as a truly
practical weapon without better engines. After the development of the heavy oil engine,
Germany jumped into the submarine business and quickly developed large overseas submarines. 
By 1913, Germany built U-Boats with Maschinenfabrik-Augsburg-Nurnberg A.G. (M.A.N.)
diesels.  The German diesel powered U-boats of pre-World WII had a speed of sixteen knots
on the surface and a range of 7,800 miles. Unlike Germany, the U.S. had significant problems
developing diesels that could provide the power, reliability, and power to weight ratio to
complete the transition of submarines from a coastal platform to an overseas fleet boat.
The U.S., like several European countries, saw the submarine as a coastal defense
weapon until World War I. After the French demonstrated the effectiveness of submarines in
breaking a blockade, the U.S. began to develop submarines for the same purpose. The U.S.
considered submarines an extension of the coastal artillery and used them as scouts. 
Submarines provided defense along the coast and protected vital shipping routes.
Submarine tactics prior to World WII called for the submarine to visually spot the target while on the surface. After locating the target, the submarine approached and attacked the target whilesubmerged at a range of 2,000 yards. This tactic placed a premium on underwater speed andbattery endurance. 9 In 1909, the General Board, the Navy's office responsible for ship

development, tended to focus more on tactical mobility, the maximum surface speed used to put
the submarine into filing position, than strategic mobility, the ability to transit to the place of
action. The smaller submarines envisioned by the Board were still considered coastal
submarines and lacked the range to stray far from home port, but maintained adequate surface
speed to attack a target.
In 1910, officers of the Atlantic Torpedo Flotilla argued for a submarine with strategic
mobility to attack enemy ships as they left their harbors.  By 1912, the Navy was beginning to
see a use for fleet submarines. Transiting with the fleet, submarines could ambush enemy
warships and cut off the enemy as they tried to break off their engagement.  As it became
apparent that the diesel engines could not support the increasing speed of the U.S. fleet, the role
of submarines changed. Submarines, placed in front of the battle fleets, would trap the enemy
fleet between the submarines and the battle fleet. 13 The development of the high frequency (HF)
radio in 1916 allowed submarines to be used as forward scouts, operating with the fleet or
independently. HF was capable of long ranges and allowed communications with boats
anywhere in the Atlantic, and later, the Pacific. Entering World War I, the U.S. submarine force
considered itself advanced and ready for war.
The submmines that entered World War I quickly learned some hard lessons. Until the
submarine first launched in 1918, submarines were considered harbor and coastal defense

units. Only the K- and L-class boats saw action in World War I and the deficiencies of their
small size quickly became apparent. The size of these coastal boats required they be towed to
England since they did not have range or reliability to cross the Atlantic by themselves. The
ability of the submarine to quickly transit to the enemy location proved to be more important
than high submerged speed. The cunent diesels lacked both speed and reliability. While U.S.
submarines did not sink any U-boats, their attempts unnerved German U-boat captains.
Submariners came out of World War I requiring bigger submarines that were better able to
survive in the Atlantic and had better habitability and range.
While the U.S. submarines did not accomplish much during World War I, the experience
the us how far behind the submarine technogy had fallen the British and The-

Germans had faster, more reliable boats with better torpedoes and periscopes. Based on the
success of the U-boat in World War I, the Navy saw the benefits of the submarine as an
offensive weapon. The German U-boats claimed ten battleships, eighteen cruisers, twenty-one
destroyers, nine submarines, and numerous merchants for a total of 5,708 Allied vessels with the
loss of only 178 out of 373 U-boats. 14 To counter the threat of the U-boat, the Allies had to
expend a considerable amount of resources and develop new tactics such as convoys and anti-
submmine warfare (ASW) planes.
During the inter period, the Navy began looking to Japan as its next likely adversary.
The Naval War College believed that, against Japan, submarines would be extremely effective in
attacking merchants and troop transports in addition to forward scouting. Due to budget
constraints and the Washington Naval Conference of 1922, the Navy lost its battlecruisers,
making the submarine the primary unit for strategic scouting. The Washington Naval
Conference also outlawed submarine blockades and the fortification of forward operating bases
in the Pacific. The loss of the ability to sink merchants in warfare was a significant blow to
submarine use, but they could still attack troop transports and other warships. 
The build-up of the Imperial Japanese Navy in the early 1930's contlibuted to the United
States' desire to build large fleet submarines capable of patrolling the Pacific. 16 Larger
submarines had the ability to stay on station longer in the vast Pacific without forward operating
 Plan Orange, the strategy war plan for defeating the Japanese Navy, assumed that the
would fall quickly to the Japanese, thereby eliminating any forward operating base.
The large distances of the Pacific dictated a submarine would travel 8,000 miles from the West
Coast to the Far East, which would take thirty-three days at ten knots. Patrols might last sixty to
seventy-five days.  Plan Orange also required submarines to travel at fast speed of seventeen
knots. Without forward operating bases the S-class, developed for the Atlantic, could not
operate in the Pacific due to the limited range and reliability issues. The S-class was ill suited
for the Pacific, as it had no air conditioning or ventilation, limiting crew endurance. The S-
class's small size created a limited range, solvable by filling ballast tanks with fuel which left
behind oil slicks once submerged. Oil slicks made the submarines more susceptible to visual
detection by smface ships and aircraft. The diesels were not powelful or reliable enough to keep
up with the fleet transit speed of twelve knots. 
In 1933, during a conference with Submarine Officers, the plans for the PORPOISE class
submarine were drawn up. The PORPOISE had diesel electric drive, eighteen knot surface speed,
an endurance of seventy-five days, and a range of 11,000 nautical miles. This design would
form the basis for all future fleet submarines that were considered multipurpose and able to
operate independently or with the fleet. U.S. submariners believed the fleet submarine would be
a tremendously useful addition to the US arsenal and an effective offensive weapon if used
properly. To contribute to the war with Japan, the Navy needed submarines with speed, range,

and endurance. To provide the required speed and endurance the submarines needed to be larger
and equipped with powerful, efficient, and reliable advanced diesel engines.
To become effective offensive weapons, submarines had to be capable of sailing at fleet
speeds, be ocean going, and have the endurance to operate far from home port. These
requirements necessitated large submarines with advanced diesel engines to power them. Power
was a critical factor to achieve increased range and endurance, the size of the submarine grew to
accommodate larger fuel tanks and increased space for crew living. The requirement for speeds
of up to twenty knots dictated the use of powerful diesel engines. These diesefs were limited to
certain revolutions per minute (RPM) by the propeller characteristics, and in size by hull
characteristics for speed.  Submarine speed was dependent on frictional resistance and wave
making resistance. Frictional resistance was proportional to surface area and wave making
resistance depended on the surface length ratio. The surface length ratio was speed divided by
the square root of waterline length. The higher the surface length ratio, the more power the
submarine required. Designers had to balance surface speed and submerged speed?  To go
faster on the smface, the hull had to be longer, which increased frictional resistance and slowed
speed, or the submarine had to be more powerful, resulting in longer and more
complex power plants. A twenty knot surfaced submarine required 5,400 horse power (HP); to
go twenty-two and a half knots, that sa:me surfaced submarine required, 9,400 HP, almost twice
the power. Designing diesels with such power proved unsuccessful due to torsional vibration, as
demmtstrated in the unsuccessful fleet sized T-class ofthe early 1920's.
submarines, where weight affects the reserve buoyancy and there is little room for
bulky engines, the power to weight ratio of diesels is extremely impmtant. Two cycle engines
have the advantage of.a power stroke each revolution of the crankshaft as opposed to once every
two revolutions for four cycle engines. Two cycle engines typically had a better power to weight
ratio than similar four cycle engines. 23 Two cycle engines, however, were less efficient than four
cycles, both mechanically and thermally. Two cycle engines with shmter power strokes
extracted less energy from the gas and the required mechanical accessories, such as the
scavenger blower drive motor, decreased mechanical efficiency. The two cycle engines ran
hotter without the cooling effect of the four cycle's intake stroke, requiring more robust cooling.
   Diesel engines needed to be reliable because critical failures of the engine on patrol made
the difference between escape or destruction at the hands of enemy warships. The inability of
submarines to carry spare parts and inadequate space to work on the engines limited the repairs
that could be done at sea. Diesel engines that went into U.S. submarines missed the mark with
underpowered, overweight, and unreliable engines untill938 when General Motors-Winton
(GM-W) and Fairbanks Morse (F-M) engines entered service. 26
The Navy did not start with diesel power in mind. The first design for a submarine was
to Holland's Torpedo Boat Co~pany~in 1895, and the-s1.1bmai1ne-was tcll)es-team

powered.27 Designers believed steam power would allow submarines to keep up with surface
ships. Designers favored steam power because of its powerful and compm·atively compact
design, seen as the only practical way to increase submarine smface speed to twenty-five knots. 28
There were several things that made steam power impractical. Once submerged, temperatures
could reach 160 degrees Fahrenheit and it took considerable time to smface and begin boiling
water for propulsion. The weight of hot water tanks and associated machinery made the
submarine heavy. Holland realized steam engines would never be successful and began looking
at alternatives. Besides gasoline engines, Holland discussed the option of putting diesels into
submarines with Colonel Edward Meier, the chief engineer of the Diesel Engine Company of
America? 9
Colonel Meier had traveled to Germru1y to test Rudolph Diesel's original working

prototype in September 1897. 30
The first U.S. Navy submarine, the USS HOLLAND, was commissioned in 1900 and
powered by gasoline, since diesel engines were not yet advanced enough for submarines. 31
Gasoline was not the ideal fuel for submarines. The volatile fuel tended to explode and the
closed environment of a submarine made the fumes especially dangerous to the crew. In 1906,
after two disastrous explosions in gasoline powered submruines, the British Navy required the
building of diesel submarines because the dangerous gasoline engines had reached their power
limit. 32 Gasoline engines were not as efficient as diesels because the gasoline mixture cannot get
as hot or dense as diesel before it pre-ignites. 33 Gasoline engines cannot produce the same
amount of power at the low RPM that mru·ine diesels can achieve.
Rudolph Diesel developed his first working engine with twice the efficiency of
conventional internal combustion engines in 1897. 34 The engine was not ready for mru·ine use
due to the complex injection system. By 1899, air blast injection or blast. injection, which used
highly compressed air to atomize the fuel to promote proper combustion, solved this problem. 35
The blast injection system added weight, additional complexity, and increased engine length due
to the addition of the compressor. The system also leaked oil past the compressor piston 1ings,
which then contacted hot air and tended to explode. 36 Preventative maintenance and increased
reliability limited the potential for explosions. In 1909, Vickers developed the solid injection
system which used fuel at an extremely high pressure, thereby eliminating the danger associated
with blast injection. Solid injection created black smoke when improper amounts of fuel were
used, something that gave away the stealthy submarine's position. Vickers' common rail
injection system, developed in 1916, controlled the strui and duration of the injection eliminating
this problem. 37 Common rail or mechanical injection came into wide use by the eru·ly 1920's. 38.
Early diesel engines, up to around 1910, had significant growing pains due to inadequate designs
and a high degree of complexity, which required skilled operators. Several companies endured
and continued to refine the engines, leading Rudolph Diesel to say in 1909, "With the help of the
diesel motor it has become possible to attack and destroy hostile navies on the high seas before
they can reach the neighborhood of the coasts and harbors."
The U.S. diesel industry started in 1898 with the Diesel Motor Company of America run
by Adolphus Busch. The mismanagement and misuse of the patent rights seemed from Rudolph
Diesel put American diesel development behind by at least a decade. 39 The first diesel engines
were four cylinder versions of a Vickers design that went into E- and F-class submarines.40
Electric Boat Company (EBC) acquired licensing to build M.A.N. two stroke diesels in 1910. 41
The EBC subsidiary, New London Shipbuilding and Engine Company (NELSECO) in Groton,
Connecticut built these early engines that went into H-and K-class submarines in 1912. The .
engine, 75/6HS, rated at 450 HP @ 450 RPM, had mixed operational reviews after successftll.
factory tests, which did not account for the shaft or how the engine was mounted once installed
in the submarine, .both of which affected vibration. 42 The test also did not adequately model the
loading and severe operating environment that the engine would be subjected to on the
submarine. Once installed in submarines, the engines exhibited crankcase explosions, scored
pistons and cylinders, broken wrist pins and air compressor valves. The Navy replaced all of the
early NELSECO engines prior to World Wru: I due to their questionable reliability. 43
To develop the skills necessary to build diesel engines the Navy sent Lieutenant Chester
W. Nimitz along with other technicians to Ge1many to work with M.A.N. The experience did
cost Nimitz a finger on his left hand, but also contributed to U.S. diesel technology for both
surface vessels and submarines.44 The second version of the NELSECO engine, used in the L-
class after several improvements, also proved unreliable. The engines suffered from clogged sea
water piping and leaking water pump glands that quickly filled the crankcase so it had to be
drained. The layout of the engine did not allow for easy repacking of the pump, so the oil level
in the crankcase had to be carefully watched to prevent the level from rising high enough to
damage the crankshaft. 45 These early engines were heavy compared to lat~r engines and tended
to fail due to deficiencies in American metallurgical technology.
was unable to copy the M.A.N. two cycle diesel~ because the U.S. lagged

behind the Germans in metallurgical technology. NELSECO had the German plans and
assistance from German engineers, but the foundries could not duplicate the casting to German
specifications. It was later discovered that the Germans only allowed the export of two cycle
technology that they were unable to perfect. The Germans used 850 HP and 1000 HP four cycle
-- . --46 -- -- --- . ------ -- -- --- -----

engines in their World War I U-boats. The Ameiicans, slow to take advantage of advances in
metallurgical technology, could not match the superior technology in casting processes, alloy
development, and heat treatments that the Germans and other European countries possessed.
The U.S. commercial foundries did not want to undertake the risky development casting of low
volume pieces, so the Navy Yards cast most of the complex pieces for the diesels. 47 As a result,
ninety percent of cylinders cast for the first NELSECO engines were rejected. 48 The resulting
engines in submarines tended to be heavier and more susceptible to failure than the German

design on which they were based, because the Germans could cast lighter, stronger, and more
complex assemblies for their engines. This disadvantage in engine technology continued until
the U.S. stopped copying the Germans and used their own designs in the mid-1930's.
After the unfavorable results with the 75/6HS, NELSECO developed a four cycle design
based on G.C. Davidson's commercial engine in 1912. The 6-EB-14, a six cylinder, 440 HP @
RPM engine, began replacing the M.A.N.-based two cycle and went into R-and 0-class

submarines. 49 The engine had a better record than the 75/6HS and was even sold to several
foreign navies including Britain and Spain. 50 The success of.the "rock crusher," as the engine
was known in the fleet, combined with the poor performance of past two cycle designs, biased
the U.S. towards four cycles until the development ofthe high speed diesel in the 1930's; 51 The
R-and 0-class remained coastal submarines because they only displaced 500 tons and were too
small for true open ocean operation. The 6-EB-14, despite its reliability, did not have the power
to propel a larger fleet submarine at the design speed of twenty knots. The request came from
the Navy in 1916 for a fleet submarine capable of twenty knots powered by 1,000 HP diesels. 52
The T -class submarines, designed to be large fleet types with the ability to patrol at long
ranges, never achieved their design speed of twenty knots. T -class submarines were obsolete by
the time they were commissioned in 1920, since the fastest battleships could tninsTt at-twenty
five knots. 53 The T-class used four larger versions of NELSECO's proven six cylinder design.
Two engines, connected to a single shaft, resulted in a powertrain 100 feet long. The unreliable
T -class engines suffered from failures of two stage injection air compressors and the heat related
failure of pistons, cylinders, and cylinder head. A weak, flexible bed plate resulted in prevalent
axial alignment problems in the long powertrain. The engines also suffered from severe
vibration issues that led to crankshaft failure. 54 The large eng~nes brought to light a problem that
plagued virtually all large diesel engines of U.S. manufacture: torsional vibration. Vibration was
a problem not a considered during the design of the T -class submarines and went unsolved until
the V-class submarines of the late 1920's.
The Navy believed an 800 ton intennediate boat similar to ocean-going German U-boats
of World War I would be sufficient for Atlantic operations. 55 The Navy ordered fifty-two of the
submarines, the majority of which were powered by NELSECO 8-EB-15 600 HP @ 380
engines. NELSECO engines were not fully developed, but EBC built the submarines

anyway. The submruines initially authorized in 1916 had so many problems the first was not
delivered until the war was over in 1918. 56 The engines had severe vibration issues due to the
critical speed that occurred a few RPM below the maximum rated power. The submarine never
reached its top speed because it was limited in RPM to prevent failures. S-1 suffered from
broken crankshafts, broken crankcase tie bolts, stripped camshaft drive gears, and stripped
jacking gear keys. These were serious failures which required significant time and effort to
repair in port. The Navy determined that NELSECO did not increase the diameter of the
crankshaft journals as was necessary when they increased the size and power of the engine. As a
quick and inexpensive fix, the RPM was lowered while the horsepower output remained
constant. 57 In addition to bearing failure, the increased loadi~g Oil the engine 1·esulted -in cracked-
heads and exhaust valve seats. The Navy eventually increased the joumal diameter which
reduced the vibration related failures and allowed for the increase of engine output to its original
specification of 600 HP @ 380 RPM. 58 NELSECO was not the only engine supplier to the Navy,
but after the fiasco with the S-class there were no more commercially developed diesels until the
s. 59
designers had to overcome the problem of torsional vibration to develop the power

and reliability needed for an effective offensive fleet submarine. The twisting of the crankshaft
during the power stroke creates torsional vibration and, as the engine reaches critical speed, the
vibrations reinforce themselves, causing destructive forces that quickly destroy the engine. 60 The
designers assumed the shaft that connected the diesels to the propellers was rigid enough so that
the absorption of vibrations could be ignored during the design process. The shaft absorbed the
engines hannonic torsional vibration and acted as a spdng, magnifying the vibrations and then
sending them back into the engine. Often the crankshaft was too weak to handle these vibrations
and failed. 61 The destructive critical speed typically occurred within the normal operating range
of submarine engines. 62 Critical speeds were first calculated in 1919 but the U.S. and other
navies managed to work around them by building heavier, stronger diesel engine casings or not
running at critical speeds. 63 The vibration problem could not be tmly eliminated until the
development of diesel-electric propulsion in the 1930's, but the problems were minimized with
stronger crankshafts, elastic couplings, different flywheels, and derating engines to keep them
from operating at critical speed.
The Navy had an excellent source of engine and submarine technology in the German U-
boat. Several officers within the submarine community believed the U.S. should take advantage
of the technologically superior captured U-boats. The Navy, however, believed il·1at-1fihe
Germans could build reliable submarines, the U.S. could as well and without copying them. The
Navy even declined plans and engineering services from Germaniawerft, Germany's leading U-
boat manufacturer. 64 U-boats could maneuver right up to the pier on diesel power, something
boats could not do because of the complex reversing mechanisms in diesels which meant

most skippers used electric power for astern propulsion. 65 The Germans had better clutches that
could be rapidly disengaged and did not bind. The significant time required for U.S. diesels to
stop and disengage the shaft made rapid diving, impmtant for submm.ines on wm.iime patrols,
dangerous. Submmines had to submerge rapidly to avoid enemy aircraft and propulsion was
needed quickly to maintain depth. The ability to crash dive was not as important during World
War I, but the U.S. realized it would become a vital skill to avoid Japanese aircraft in the Pacific ..
The USS JACK (SS-259), a fleet boat commissioned in 1943, trained to a wartime crash dive
of thirty seconds, a time measured in minutes on S-class boats in the 1920' s 66 The U-

boats also had superior engines. One captured U-boat, compared directly against the S-3, tumed
out to be three knots faster. 67 The captured U-boats were so reliable and easy to operate that,
when they cruised from Germany to the West Coast with unskilled mechanics, they suffered no
failures. fu one U-boat engine disassembled after 25,000 miles of service, the machining marks
were still visible on the internals of the oil pump, which frequently failed on S-class
submarines. 68 The Navy could clearly benefit from the technologically superior engines in the
even if they did not copy other aspects of the submarine.

The Navy needed a reliable diesel engine source and since U.S. domestic manufactures
could not produce a reliable design or copy, the Navy Bureau of Engineering began to design
their own. The Bureau began building copies of the M.A.N. engines in captured U-boats, but the
lagged so far behind in metallurgical technology that the New York Naval Yard (NYNY)

could only build detuned engines weighing ten percent more than the copied engines. 69
Beginning in 1919, Bureau-M.A.N. engines rated at 1000 HP@ 425 RPM, heavier copies of
M.A.N. six cylinderS 6 V 45/42 1200 HP@ 450 RPM diesels, replaced NELSECO engines inS
and V-class submarines.70 By 1930, the Bureau of Engineering, confident in its engines, rated
them at their designed power, comparable to what the Getmans used thirteen years earlier.

Submarine o-10

USS O-10 (SS-71) was an O-class submarine of the United States Navy. Her keel was laid down on 27 February 1917 by the Fore River Shipbuilding Company in Quincy, Massachusetts. She was launched on 21 February 1918 sponsored by Mrs. John E. Bailey, and commissioned on 17 August 1918 with Lieutenant Sherwood Picking in command.

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