3-inch gun M1903

M1903 gun
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
Specifications
Mass	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 firing range	11,328 yd (10,358 m) at 16° elevation
Maximum firing range	11,328 yd (10,358 m) approx.
Feed system	Manual
Sights	Telescopic

The 3-inch gun M1903 was a rapid-fire breech-loading weapon, with 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 boast 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.

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.

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.

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.

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 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.

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

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

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.

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.

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.

Ammunition

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.

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.

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.

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:

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.

Specifications

Specifications from TM 9-421

3-inch Gun M1903
Length, total over-all	175 inches
Length of bore	50 calibers
Maximum diameter of chamber	4.31 inches
Weight, including breech mechanism	2,690 pounds
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 inches
Depth of groove	0.03 inches
Width of land	0.10 inches
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 feet 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 inches
Maximum traverse	360 degrees
Pedestal, outer flange diameter	42 in (1,067 mm)

Dependent upon construction and emplacement

Where used

The 3-inch gun M1903 was used at several coastal forts that were built under the recommendation of the Endicott board. The gun was mounted in forts and batteries per the following list:

3-inch Gun M1903

Fort	Battery