Table Of ContentDefinitions and Information about Naval Guns - Part 1
Definitions and Information about Naval Guns
Part 1 - Weapons and Mountings
By Tony DiGiulian
Updated: 10 July 2006
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Ammunition,
Mounting /
Gun Gun Fuze and Miscellaneous
Turret
Nomenclature Definitions Projectile Definitions
Definitions
Definitions
Gun Nomenclature
General
Naval Guns are usually classified by "caliber" (diameter of the bore), "calibers" (length of the barrel described in multiples of the diameter of the bore)
and usually a "Model" or "Reference" designation and occasionally a modification indicator.
For example, the description: USN 16"/50 Mark 7 Mod 0
Means that the gun was developed by the Navy of the United States of America, has a bore 16 inches (40.64 cm) in diameter, a barrel length of 16 x 50
inches = 800 inches (20.320 m) long and is the seventh version of the 16 inch gun with no modifications to the original Mark 7 design.
The way barrel length is measured may differ between nations and sometimes gun types. Please see "Barrel Length / Bore Length" below. Generally
speaking, the longer the barrel, the more powerful is the gun.
Gun and Mounting Designations of the Major Naval Powers
British Designations
In the latter half of the 19th century, British cannon designs made a gradual transition from muzzle loading rifles (MLR) to breach loading rifles (BLR).
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Any breech loader of that period which could fire faster than about two rounds per minute was known as a "quick fire" (QF) cannon, whether it used bag
ammunition or cartridge ammunition. However, by the early part of the twentieth century, the BL designation was given only to bag guns while the QF
designation was used only for cartridge guns. This separation into BL and QF categories was carried into the designation system, with BL and QF guns
of the same caliber being enumerated into different numeric series. Except in gun lists, QF guns were not usually subdivided into separate and fixed
ammunition types. Gun designations during this time were per the diameter of the bore in inches or, for smaller guns, by the nominal weight of the
projectile in pounds. A few guns, mainly those developed abroad, were designated by the manufacturer and the bore size in millimeters, such as the
Bofors 40 mm and the Oerlikon 20 mm. The bore size was followed by the BL or QF designation and a Mark number using Latin numbers, sometimes
followed with one or more asterisks or stars which indicated minor modifications to the original design. For example, the designation 4-in QF Mark XVI*
meant a cartridge gun firing a 4 inch (10.2 cm) projectile, with the design being the sixteenth gun in the 4 inch QF series and having had one minor
modification to the original design.
Many, but not all, larger-caliber weapons designed for the British Army were given mark numbers in the same series as naval guns of that caliber, a
practice which occasionally leaves a "hole" in the naval mark number series. I do not usually include a data page for such Army-only weapons, but
instead put a "Nomenclature Note" on an appropriate datapage to account for these "missing" mark numbers.
For guns with fractional inch bores, the British practice was to place the decimal point directly under the inch symbol followed by the tenth inch value, a
combination not readily reproducible with modern type fonts. Roughly, this would appear as 4."5 for a 4.5" (11.4 cm) gun. For clarity, I show all such
designations as 4.5" (11.4 cm).
Naval mountings had a separate designation, usually incorporating the type of mounting into the designation, and enumerated by the gun caliber. For
example, 4.7-in CP Mark XIV meant that the mounting was for 4.7-inch (12 cm) guns, was a "Center Pivot" type, and was the fourteenth mounting in the
CP series used for 4.7-inch (12 cm) guns. Similar to guns, asterisks were used to show modifications to the original design, with each additional asterisk
identifying a separate modification. A few smaller mountings were designated by their total weight. For example, the 12-pdr 18-cwt was a designation
given to a mounting for a 3-inch (7.62 cm) gun firing a 12-pound (5.4 kg) projectile and the gun and mounting together weighed 18-hundredweight or
about 2,016 lbs. (914 kg).
Up until shortly after the end of World War II, British weapons were almost always known by their gun designation and not by the designation of the
mountings in which they were used. For example, the designation of the famous 15-in Mark I was for the gun itself, not for its mounting. However, in
1950 the British weapon designation system was changed such that weapons were now known by the designation of the mounting that they were used in
and not by the designation of the gun itself. At this same time, Roman numerals were dropped in favor of Arabic numerals.
Some confusion was created under this new designation system as many older weapons were redesignated, even though the weapons and mountings
themselves did not change. For example, the weapons used on the Daring class destroyers of the late 1940s were 4.5-in Mark V guns and these were
used in 4.5-in Mark VI twin mountings. Under the old designation system, these weapons were referred to as being the 4.5-in Mark V, in other words,
by the designation of the gun itself. Under the new system, the guns and mountings together were now referred to as being the 4.5-in Mark 6, which had
previously been just the mounting designation. In an effort to reduce confusion, both the original and subsequent designations are given on my data
pages for these redesignated weapons, with the newer designations shown in parenthesis.
Under this new designation system, modifications were also now given arabic numerals rather than asterisks, although asterisks were brought forward
for those guns having additional modifications after being redesignated. For example, the 4.5-in Mark IV guns and 4.5-in Mark V mountings taken from
scrapped "C" class destroyers and then modified and reused on the Tribal class frigates (Type 81) built in the 1950s were now designated as 4.5-in
Mark 5* Mod 2 meaning that these mountings had been modified once prior to the change to arabic numbers and twice afterwards.
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Guns designed post-war were now designated with an N (apparently for "Navy") such as the 6-in QF N5 used on the Tiger class cruisers in Mark 26 twin
mountings.
After Britain adopted the metric system in 1965, naval guns and mountings were reclassified in metric units, although English units are still commonly
used for many weapons even to the present day.
Note that none of these designation systems include barrel length (calibers) in the designation. For purposes of clarity, I have included barrel length for
all gun designations on my British data pages, but strictly speaking, it is incorrect to do so.
Additional information may be found in the Naval Technical Board essay Pounders!
French Designations
Individual guns are identified by the bore in millimeters, the length in calibers of the bore and the year design was started. For example, the designation
380 mm/45 M1935 meant a gun whose design was started in 1935, firing a 38 cm (14.96-inch) projectile and whose bore length was 38 x 45 cm long -
17.100 m (673 inches). Mountings were designated with the Model Year, for example, M1932.
Some USA weapons were in French service for a brief period following World War II, but most have been produced by France and follow the above
designation system.
German Designations
The methodology of German Naval Gun designations changed three times in the first half of the 20th century. In the period before and during World War
I, German guns were designated by their bore diameter in centimeters, "SK" meaning naval cannon, and their nominal overall length. So, for example,
the designation 30.5 cm SK L/50 meant a naval gun firing 30.5 cm (12.008-inch) projectiles with a barrel whose overall length was 30.5 x 50 cm long -
1525.0 cm (600.4 inches). The second method was for guns designed in the 1920s through 1940 where the length figure was dropped in favor of the
Construction Year (Model Year). Under this system, the guns carried by the Bismarck were designated as 38 cm SK C/34 meaning that these were
naval guns firing 38 cm (14.96-inch) projectiles whose design was started in 1934. The third method was adopted in 1940 and under this system guns
were designated by their bore in centimeters, "KM" meaning naval cannon and the design year. For example, the designation 10.5 cm KM44 was for a
10.5 cm (4.1-inch) naval gun designed in 1944.
Note that neither of these last two systems included barrel length (calibers) in the designation. For purposes of clarity, I have included barrel length for
all gun designations on my German weapons data pages, but strictly speaking, it is incorrect to do so for weapons designed after 1918.
Gun Mountings were designated with the type of mounting and the year of design. For example, the designation Drh Tr C/25 was for a turret mounting
whose design was started in 1925.
Many postwar guns are foreign designs and are commonly known by the designation given by the producing nation.
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Additional information may be found in German Ammunition, Guns and Mountings Definitions.
Italian Designations
Prior to the 1920s, most large caliber guns and many smaller caliber guns were imported from Britain. For that reason, most of these guns were
designated in inches. Guns developed in Italy after that time were identified by their bore in millimeters, the length in calibers of the bore and the year
design was started either on the gun itself or on the mounting. For example, 135 mm/45 Model 1938 was the designation given to the guns used on the
"Capitani Romani" class small cruisers and these were used in Model 1938 turrets. Often the manufacturer's name was also included as part of the
designation. Mountings designed by the Italian Navy rather than by a manufacturer were given an RM designation, which stood for "Regia
Marina" (Royal Navy).
Some USA weapons were in Italian service following World War II, but most post-war guns have been produced by Italian armament firms and generally
follow the above designation system.
It should be noted that many Italian-produced naval guns even to the present day have been to English measurement units, not metric. For example, the
main guns on the Littorio class battleships had a bore of 381 mm (15.00 inches), not 380 mm (14.96 inches) as did their French and German
contemporaries. Likewise, the modern-day 76 mm Compact has an actual bore of 76.2 mm (3.00 inches).
Japanese Designations
The formal gun designation dating from the beginnings of the Imperial Japanese Navy was made up of the barrel or bore length in calibers (kôkei), a type
year (shiki) based upon when the design of the breech mechanism was begun, the bore diameter and finally the suffix hô (gun). For example, the
designation 40 caliber 14 cm 11 Year Type Gun would mean a 14 cm/40 (5.5") gun whose breech design was in the 11th year of the Taishô regnal era
(1922 A.D.). Imported weapons had an additional designation to indicate the manufacturer.
Following the methodology of their British mentors, bore length was measured starting from the top of the mushroom head (vent axial) of the breech
block for bag guns and starting from the inner breech face for cartridge guns. For a few guns, the bore length designation was actually the overall length
of the barrel.
Prior to 5 October 1917, the bore diameter was measured in English units. Guns with fractional inch bores followed British practice and were designated
such as 4 in 7 (4.7 inch - 12 cm) and 5 in 5 (5.5 inch - 14 cm). For clarity, I list these as decimal values, in these instances as 4.7" (12 cm) and 5.5" (14
cm). On 5 October 1917, the Japanese Navy converted to the metric system and most naval guns were then designated with the bore diameter rounded
up or down to a whole centimeter number, but not necessarily to the nearest value. For example, 8 cm rather than 7.62 cm for 3.0-inch guns, but 30 cm
rather than 31 cm for 12.0-inch guns.
The shiki designations (Type Year, which can be considered as the Model Year) are quite complicated. On 25 December 1908, which was the 41st year
of the Meiji regnal era, the designations of all guns in service in the Imperial Navy were modified. Weapons that had been manufactured by the
Japanese were designated as 41 shiki hô (41 Type gun or Model 1908) even though most of them had been designed and produced prior to 1906.
After this time, the Type Year was based upon when the design of the breech mechanism was begun. Two different calendar systems were used to
define the Type Year. Between 1908 and 1927, the Type Year was based upon the year of the current regnal era, followed by the suffix nen (year), such
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as 11 nen shiki (11 Year Type or Model 1922). Those guns produced between 1927 and 1939 were assigned Type Years using the last two digits of the
Imperial Calendar year, which dated from the start of the reign of Emperor Jimmu in 660 B.C., with 1927 A.D. being Imperial Calendar Year 2587.
Finally, under the Imperial Calendar system, weapons designed between 2600 and 2605 (1940-45) were designated by using just the last digit of the
Imperial year. All of these Type Years should be used with caution, as there are cases where the breech mechanism design is much older than the
design of the rest of the gun. So, guns with the same Type Year designation may actually have been developed many years apart.
It should also be noted that these Japanese Year Type designations do not translate well into English. For example, although a literal translation of 11
nen shiki hô would be 11 Year Type Gun, this sounds "wrong" to English-speakers. For that reason, most English translations of this designation
would show it as either 11th Year Type or as Type 11. Neither of these are literally correct translations, but sound "better" to English-speakers. On my
data pages, Japanese designations are shown such as 11th Year Type for regnal-era guns and such as Type 94 for Imperial Calendar-era weapons.
As noted, these are not literally correct, but I believe them to be more easily understandable by English speakers.
As examples of Japanese designations for naval guns:
l Under the regnal era and metric systems, the Japanese-built main guns carried by the Kongo class were formally redesignated on 5 October 1917
as 45 caliber 41 Type 36 cm - 36 cm/45 Model 1908 - even though the bore size was actually 35.56 cm (14.0-inch), the original design by Vickers
dated from 1910 and no guns were produced in Japan before at least 1912.
l Under the Imperial Calendar system, the AA guns carried by the Agano class cruisers were designated as 60 caliber 98 Type 8 cm - 8 cm/60
(3.15-inch) Model 1938. However, these guns actually had a bore size of 7.62 cm (3.0-inch).
l The British 2-pdr gun made by Vickers and exported to Japan in the 1930s was designated as 62 caliber 91 Type 40 mm "HI" - 40 mm/62 "HI"
Model 1931, where "HI" (also translated as "BI") was the designation meaning Vickers. This designation is notable for using the overall barrel
length rather than the more common Japanese method of being per the bore length, which was 39 calibers, identical to other Vickers 2-pdr. guns.
Weapon systems other than naval guns were primarily designated as to when they entered service. For example, the famous Zero fighter plane of
World War II derived its name from its designation, Type 0 carrier-based fighter, as its service introduction was in the Imperial Calendar year 2600
(1940).
It should be noted that the Japanese Model number system became chaotic towards the end of World War II. New weapons were assigned Model years
that had no relationship to the actual Type year, with some apparently chosen simply to fill in missing years in the series. As John Campbell put it, "such
are the pitfalls of Japanese ordnance [nomenclature]."
On my data pages, the Type Year in A.D. is always noted and all known designations that a weapon had during its service life are listed.
Postwar guns are primarily foreign designs and are commonly known by the designation given by the producing nation.
Additional information may be found in Japanese Ammunition, Guns and Mountings Definitions.
Russia / USSR Designations
Prior to 1917, designations included the bore size, overall barrel length and the Obrazets - Pattern (Model) Year. Guns were designated either by their
caliber in inches if it was a whole number or in millimeters for all others. The Pattern Year was the date the weapon was accepted into service. After
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1917, a project number was added and all calibers were designated only in millimeters. As an example of the post-1917 designation system is 130
mm/50 B13 Pattern 1936, which meant that this was a weapon firing 130 mm (5.1-inch) projectiles, had a barrel 50 calibers long, was designed at the
"Bol'shevik" plant as Project 13 and which entered service in 1936.
United States of America Designations
Up until just after World War II, each caliber of USN guns was identified by a mark number, its length in calibers and a modification number, the original
modification designation being "Mod 0". For example, 16"/50 Mark 7 Mod 0 meant a gun firing 16-inch (40.64 cm) projectiles with a barrel 16 x 50 = 800
inches (20.320 m) long, was the seventh gun in the 16-inch (40.64 cm) series and was built to the original design with no modifications. A few smaller
guns built or purchased mainly in the latter part of the 19th century were known by the weight of their projectiles; the 1-pounder through 6-pounder.
Roman numerals were used for many designations until about 1920 when arabic numerals were substituted.
Gun Mod numbers generally indicated changes to the original design for new guns or a change made to a finished gun. For example, a change in the
rifling pattern from the original design might be designated as Mod 1 and new guns built with this rifling would be so designated. Mod 0 guns being
relined with this new pattern would also then be designated as Mod 1.
Mountings originally had a similar designation, being of the form 12" Mark 8 Mod 0 for a mounting using a 12-inch (30.5 cm) weapon. By 1930, the Mark
number mounting designation had been dropped for weapons larger than 5 inches (12.7 cm) and new mountings were then known by the ship class they
were used on. For example, the 16"/50 (40.64 cm) guns used on the Iowa class battleships were designated as Mark 7, but the mountings for them were
designated as 16-inch three-gun mountings Iowa class. Mountings for 5 inch and smaller guns continued to have Mark numbers assigned to them.
Similar to Britain, shortly after World War II the USN designation system was changed from being based upon the gun classification to being based upon
the mounting classification. So, a modern designation such as 5"/54 Mark 45 is really the designation of the gun mount, not the weapon itself.
Furthermore, starting with the 5"/54 Mark 42, almost all naval guns are now classified into a single "Mark" series, regardless of their caliber. For
example, modern guns such as the 5" Mark 45, the 76 mm Mark 75 and the 57 mm Mark 110 are all in the same numeric Mark series.
Additional information may be found in USN Naval Gun Designations.
Gun Definitions
AA - Anti-Aircraft.
AAA - Anti-Aircraft Artillery. Refers to larger caliber guns used as anti-aircraft weapons, usually any AA gun larger than about 2.5 in (6.4 cm).
AA/Su - Anti-aircraft/Surface. British designation used to denote dual-purpose weapons or fire control systems. This replaced the previous "HA/LA"
designation in 1947.
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Autofrettage - A process in which a favorable distribution of initial or residual stress in a tube is induced, as in the manufacturing of gun barrels. Literally
means "self-hooping" and the process involves expanding a partially machined barrel or liner by applying hydraulic pressure to the interior surface. The
metal of the bore is the first to be stretched beyond the elastic limit. The process is continued until the metal at the outer surface just reaches its elastic
limit. At this point, the increase of hydraulic pressure in the bore is halted and soon afterwards the pressure is reduced to zero. Since the metal at the
bore has received a certain amount of plastic deformation, it would, if left free to do so, retain all of this "set." However, since the metal at the outer
surface has received no permanent set, but only a strain within the elastic limit, it attempts to return to its original diameter. The metal between the bore
and the outer surface has received some plastic deformation, decreasing outward. The final result is that the bore is forced back to a diameter
somewhere between the original diameter and that which was attained under the maximum hydraulic pressure. Thus, the bore has received a certain
amount of tangential tension, exactly as in the case of a built-up gun, but with the difference that the autofrettage process results in a indefinite number of
layers, each infinitesimal in thickness, and having varying stresses which result in producing the maximum possible strength in the finished gun. This
process allows steels with low alloy content to be used to make gun barrels. During the 1920s and 1930s, the US Navy termed this process
"manufacture by radial expansion."
Bag Guns - Weapons that used powder bags rather than a cartridge to hold the propellant. This was the most common ammunition type of the twentieth
century for 6 inch (15.2 cm) and larger guns. Guns using powder bags were designated as "Separate Loading" in the USN, a reference to the normal
procedure for bag guns of first ramming the projectile and then the powder bags. Smaller calibers generally use a single bag while larger calibers may
have as many as six bags. See "Bag Ammunition" on the Ammunition Definitions data page for additional information.
Bayonet Joint - An interrupted-thread method of attaching the gun
barrel to the housing in order to make for easier barrel replacements.
For many USN guns designed for case ammunition, the housing took
the place of the yoke and screw-box liner used on bag guns. This
construction method allowed the elimination of the slide cylinder in
some weapons.
Barrel Length / Bore Length - One of the more confusing items about gun designations is that the way that the length (calibers) of a gun barrel is
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measured differs from nation to nation. The USA measured starting from the inner breech face for both bag and cartridge guns. Austria-Hungary
(Skoda), Germany and Russia measured the length of the entire barrel. Britain, France, Italy, Japan and Sweden (Bofors) measured starting from the
top of the mushroom head (vent axial) of the breech block for bag guns and starting from the inner breech face for cartridge guns. These differing
methods have often resulted in errors in reference works. For example, the 38 cm SK C/34 guns on the German battleship Bismarck are often noted as
being 47 calibers long. Per the German method - overall barrel length - these guns were 51.66 calibers long and per the British/USA method - measured
from the inner breech face - they were 48.3 calibers long. As every German document I have seen refers to these guns as being the equivalent of either
51.66 or 52 calibers long, I am not certain why so many authors refer to these guns as being 47 calibers long. My thanks to M.J. Whitley, whose series
of books on German Warships of World War II first enlightened me on how the German methods differed from those of other nations. On my webpages,
"Gun Length oa" refers to the overall barrel length. "Bore length" is per each nation's specification except where noted.
BL - British designation meaning Breech Loading cannon. In the 1800s the the British used the designation BLR where the "R" stood for Rifle, but after
about 1890 the "R" was dropped from new gun designations. By the early part of the twentieth century, BL had become to be used only for bag
ammunition guns.
BM - Breech Mechanism.
BMG - Browning Machine Gun. These were recoil-operated machine guns of various calibers originally designed by the USA inventor John Moses
Browning (1855 - 1926), the most famous being the "fifty-caliber." The modern version is the 0.50" (12.7 mm) BMG M2HB, with M2HB meaning Mark 2
Heavy Barrel. The M2 designation is why this weapon is often known as the Ma Deuce.
Bolt - The mechanism that positions the cartridge in breechloading guns, closes the breech, and ejects the spent cartridge.
Bolt Open or Open Bolt - Refers to automatic or semi-automatic weapons that are designed such that the gun bolt is normally held to the rear of the
weapon, leaving the breech open. Only after the trigger is activated is the next round pushed into the firing chamber and the breech closed. This design
reduces the chances of an accidental "cook off" as no bullet is in the firing chamber until after the trigger is activated.
Bolt Closed or Closed Bolt - Refers to weapons that are designed to hold a bullet in the firing chamber with the bolt closed prior to activating the trigger.
Bore - Inner Diameter (ID) of the barrel. This is measured from land surface to diametrically opposed land surface. For example, the USN 16"/50 (40.64
cm) guns used on the Iowa class battleships had a new gun land to land diameter of 16.00 inches (40.64 cm) while the diameter as measured from the
bottom of the groove to the opposite bottom of the groove was 16.30 inches (41.40 cm). "Bore" is also used as a shorthand reference for "Bore Length" -
see "Barrel Length / Bore Length" above.
Breech - The rear of the gun. In most 20th century guns, where the shell goes in, hence the name "Breech Loader."
Breech Block, Breech Mechanism or Breech Plug - This is the
mechanism at the rear of the gun which closes the bore against the force
of the firing charge. For large weapons, such as a battleship's main guns,
these are usually of an interrupted-screw construction, which gives a very
strong seal. For rapid fire guns, a sliding breech-block is commonly used
which may open and close automatically as the gun is fired.
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Breech, Four-Motion - Early screw breech design invented by the French where all of the threads were at the same level. Usually there were five or six
threaded sections separated by equal width non-threaded sections. These breech blocks were comparatively long as half of the thread was cut away to
allow withdrawal, thus reducing their capacity to withstand firing stresses. This type of breech mechanism required that the block be first withdrawn
straight back from the gun barrel before it could be moved out of the way of the reloading process and some had to be disconnected entirely from the
gun. Closing the breech was a complicated operation, involving four motions: swing the carrier so that the screw could enter the breech, slide the entire
breech mechanism forward so as to seat it, turn the screw through part of a turn until the threads meshed with those in the breech, and then lock the
mechanism.
Breech, Pure-Couple - British Welin Breeches of the early 1900s that used a long, manually operated lever to operate the breech screw. See "Breech,
Welin" below.
Breech, Single-Motion - See "Breech Mechanism, Smith-Asbury" below.
Breech, Three-Motion - Similar to a Four-Motion Breech, except that the breech was withdrawn into a hinged carrier ring. This meant that the motions
were reduced to unlocking, withdrawal and then swinging out of the way.
Breech, Welin - A stepped-thread breech developed during the 1890s
and named after the inventor, Axel Welin, a Swedish Ammunition
Engineer then residing in London. A Welin breech block has only one
third or one quarter of the threads removed, which means that a
shorter screw length can be used to obtain the same strength as a
four-motion breech mechanism. See the "breech plug" in the
illustration above for a typical Welin design. Unlike the four-motion
breech, a Welin breech allows the mechanism to be simply unscrewed
and swung out of the way, it does not have to be withdrawn straight
back from the gun barrel. Variations of the Welin Breech design were
used on most bag ammunition guns of the twentieth century.
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Breech Block, Vertical Sliding-Wedge - Used on many cartridge guns, this sort of breech mechanism slides vertically in grooves cut in the housing.
After the cartridge is inserted, the breech block slides up with the sloping part of the forward face wedging the cartridge case home in the chamber. An
extractor mechanism catches the cartridge rim as the breechblock drops after firing, pulling the expended cartridge out of the gun. A few guns use a
similar design, but with the breechblock sliding horizontally. These, of course, are known as "Horizontally Sliding-Wedge" breechblocks.
Breech Mechanism, Smith-Asbury - Introduced in 1916 and named after its inventors, Lt. Cmdr. George Leonard Smith, USN and Draftsman Dorsey
Frost Asbury, both of the Naval Gun Factory at the Washington Navy Yard. This mechanism used gearing to fully open a Welin breech by linking the
unscrewing, withdrawing and swinging clear movements into one continuous action and for that reason is sometimes known as a "single motion" breech
mechanism. The breech threads are undercut at the start so as to allow the block to swing into position.
Built-up Construction - Guns that are manufactured from multiple hoops (tubes) which are joined together with locking rings and overlapping sections
to make longer and/or thicker sections. This was the most common process for manufacturing almost all guns until the 1920s when monobloc
techniques were introduced for guns smaller than about 6 inches (15.2 cm). See "Monobloc" and "Wire-Wound" below.
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