Military Wiki
M1903 gun
M1903 3 inch Gun.png
3-inch Gun M1903
Type Rapid-fire seacoast gun
Place of origin United States
Service history
In service 1903 - 1940s
Used by USA
Wars World War I and World War II
Production history
Designed 1903
Variants M1903, M1903MI
Weight gun & breech 2,690 lb (1,220 kg)
Barrel length 175 in (4.4 m)

Shell Fixed ammunition, 15 lb (6.8 kg) shell
Caliber 3-inch (76.2 mm)
Action Hand operated
Breech slotted screw
Recoil hydro - spring, 45 inches (1.14 m)
Carriage Pedestal
Elevation -5° - +16°
Traverse 360°
Rate of fire 12 Rounds /minute
Muzzle velocity 2,800 ft/s (850 m/s)
Effective range 11,328 yd (10,358 m)
at 16° elevation
Maximum range 11,328 yd (10,358 m) approx.
Feed system Manual
Sights Telescopic

The 3-inch gun M1903 was a rapid fire breech-loading artillery gun with a 360-degree traverse. The M1903 gun was an improvement of the M1902 seacoast gun. The 3-inch gun was placed to provide fire to protect submarine mines and nets, and to protect against motor torpedo boats within its range. The 3-inch gun was mounted on a pedestal mount that bolted into a concrete emplacement that provided cover and safety for the gun's crew.[1]

Design and construction

3-inch Gun M1903

The gun barrel is of the built-up type. The jacket fits over the rear end of the tube and projects beyond it. The breech bushing is screwed into the end of the jacket and the breech mechanism is assembled into the bushing. The breech bushing bears interrupted threads for the breechblock.[1]

Breech mechinism

The function of the breech mechanism is to close the breech, and thereby hold the cartridge case in place. The breechblock is the main part of the mechanism. It closes the breech and is hinged so that it can be swung open for loading. It is moved by an operating lever. The lever and breechblock are connected by an operating bar, operating in a T-slot in the breechblock carrier. Thus connected, complete motion of the operating lever to the right will cause the breechblock to rotate and to be swung clear of the breech recess. Swinging the operating lever fully to the right engages cam surfaces of the breechblock carrier and extractor, causing the extractor to eject the empty cartridge case.[1]

Firing mechanism

The firing mechanism is known as the continuous pull, percussion type; that is, no cocking of the firing pin is required other than a pull on the lanyard or trigger shaft.[1]

Pedestal Carriage M1903

The gun carriage consists of a pedestal, bolted rigidly to the concrete emplacement, and of a gun-supporting structure, which rests on the pedestal and is capable of traversing upon it. The pedestal is the foundation piece of the gun carriage. On the M1903 carriage the pivot yoke is mounted in the pedestal and rests upon a ring of ball bearings on the base of the pedestal. The entire weight of the gun and top part of the carriage rests upon this ring of ball bearings. The bushings for the pivot yoke form two supports against the thrust of firing. At the upper end of the pivot yoke, on either side, trunnion bearings are provided for the cradle trunnions. The shield and shield supports are bolted to the pivot yoke. The opening for the gun in the shield is prolonged underneath to allow for the removal of the piston and springs from the recoil cylinder.[1]

The carriage consists of recoil and counterrecoil mechanism, elevation mechanism and traversing mechanism. In addition, the M1903 carriage has a range drum.[1]

A recoil cylinder checks the recoil of the gun, and a spring inside the recoil cylinder returns the gun to battery.[1]

On the M1903 carriage a friction band is provided and is adjusted so as to allow a certain amount of friction between itself and the traversing rack.[1]

Gun crew

A gun battery consists of one or more gun emplacements, and is under the command of the battery commander. The battery commander is assisted by a battery executive and an assistant battery executive. These positions are filled by officers.[2]

Each gun in an emplacement is manned by a gun section consisting of a gun squad of 15 (war strength) or 12 (peace strength) enlisted men including one noncommissioned officer, the chief of section, and an ammunition squad of 9 (war strength) or 6 (peace strength) enlisted men including one noncommissioned officer, the chief of ammunition.[2]


The ammunition for this gun is fixed and of a weight that can be handled entirely by hand. The ammunition is brought from the magazine to the gun and held ready for loading. To load, push the shell home into the breech recess of the gun with a moderately quick motion of the hand.[1]

Ammunition for the 3-inch gun M1903 is issued in the form of fixed complete rounds. The term "fixed" signifies that the propelling charge is fixed (not adjustable) and that the round is loaded into the gun as a unit. The propelling charge is assembled loosely in the cartridge case which is crimped rigidly to the projectile. A complete round of ammunition comprises all of the components necessary to fire one round.[1]

Dependent upon the type of projectile, ammunition for these guns is classified as high explosive, target practice, blank, or drill. The high explosive projectile contains a high explosive filler. The target practice projectile contains no explosive; it consists of either a solid projectile (designated shot) or a heavy-walled projectile with an empty base cavity. The blank ammunition has a black powder (low explosive) charge in the cartridge case and no projectile. The drill ammunition consists of completely inert cartridge which simulates the service ammunition.[1]

All projectiles are painted to prevent rust and corrosion and by the color to provide a ready means of identification as to type. The projectiles of the ammunition described herein are painted as follows:[1]

3-inch Gun M1903
Round Color Marking
High explosive Yellow black
Practice (Projectile is inert.) Black White
Drill or dummy (Round is inert) Black White

Note that the above color scheme is not wholly in agreement with the basic color scheme, described in TM 9-1900, practice projectiles being generally painted blue.[1]


Specifications from TM 9-421[1]

3-inch Gun M1903
Length, total over-all 175 in (4,445 mm)
Length of bore 50 calibers
Maximum diameter of chamber 4.31 in (109.47 mm)
Weight, including breech mechanism 2,690 lb (1,220 kg)
Type of construction Built-up
Rifling:Twist R.H. increasing from 1-50 at origin to 1-25
Number of grooves 24
Width of groove 0.2927 in (7.43 mm)
Depth of groove 0.03 in (0.76 mm)
Width of land 0.10 in (2.54 mm)
Type of breechblock Slotted screw
Type of breech mechanism Lever pull
Number of handles to operate 1
Power Hand
Type of firing mechanism Continuous pull
Muzzle velocity, maximum 2,800 ft (853 m) per second
Range, maximum:
(Using Shell, H. E., M42 and M42A1) 10,943 yd (10,006 m)
(Using Shell, H. E., 15 lb, M1915) 11,328 yd (10,358 m)
(Using Shell, H.E., MK1) 9,177 yd (8,391 m)
Life of gun (full charge) 2,500 rounds
Rate of fire (normal) 12 rounds per minute
Rate of fire (maximum) 30 rounds per minute
Carriage, 3-inch M1903
Type Pedestal
Total weight 3,310 lb (1,501 kg)
Elevating mechanism:
Type Screw
Power Hand
Speed Variable
Maximum elevation +16 degrees
Minimum elevation -10 degrees
Traversing mechanism:
Type of bearing Ball
Mean diameter of roller path 3.3 in (83.8 mm)
Maximum traverse 360 degrees
Pedestal, outer flange diameter 42 in (1,067 mm)

Dependent upon construction and emplacement[1]

Where used

The 3-inch gun M1903 was used at most of the coastal forts that were built under the recommendation of the Endicott Board. The number of guns in each battery varied from one to four. The number of batteries in a fort also varied; many forts had only one 3-inch gun battery, while some had as many as four.

See also



  • War Department TM 9-421 3-Inch Seacoast Gun Materiel
  • War Department FM 4-90 seacoast artillery: service of the piece, 3-inch rapid-fire gun

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