Submarine Guns

Submarine Guns 1900-1945

For the first 16 years of USN submarine operations, guns were not considered to be a useful weapon on a ship designed for a stealthy submerged attack. In fact, no USN submarine carried a deck gun until the M-1 (Submarine No. 47) of 1916. The L-class of 1914 were also designed for it, but it had to be retrofitted to the early boats as the gun was not ready when the first boats were laid down. Simon Lake's Protector of 1903 briefly carried a Hotchkiss Mk 1 1 pdr/20 caliber gun in an "armored sighting hood" atop the conning tower, but that boat was never commissioned into the USN and the idea did not catch on in the service for several more years.

It is likely that submarines from the C-class on carried small arms for self defense while in port. These would have included the Colt M1892 and M1909 revolvers for officer use, and eventually the famous M1911 and M1911A1 pistols. Rifles would have been Krag-Jorgensen M1896/M1898 and Springfield M1903 models. The number of variations for these weapons is large, and small arms of these types will not be listed here.

By late 1912 it was realized that a deck gun of some sort might prove useful to submarines if they were forced to surface in the midst of small enemy picket and patrol vessels, and to potentially finish off already crippled targets. Equipping submarines with guns was also a trend among European navies. When the L-class bidder's package was developed by the Bureau of Construction & Repair (BuC&R) a proviso was written into it for a small deck gun. Underwater performance was still highly emphasized at this time, so it was stipulated that the gun be retractable to limit underwater drag.

The weapon chosen was the 3"/23 caliber Mk 9. This semi-retractable dual-purpose (both anti-surface and anti-aircraft) gun became the standard for several submarine classes designed during WWI, but in practice it was found to be lacking in hitting power. Experience in WWI showed the usefulness of a deck gun in submarine operations, and with the exception of the diminutive N-class all subsequent submarines in the USN were equipped with deck guns.

A major issue facing the use of deck guns on submarines was corrosion and rusting. The gun is constantly wet, even while on the surface, and the ever changing air-to-water environment is the perfect condition for destructive corrosion and rusting to set in. Constant and detailed maintenance was required in order to keep the gun operational. Even with the use of corrosion-resistant materials like stainless steel and brass maintenance was a never ending chore. The barrel interior liner with its rifled grooving was particularly susceptible to corrosion damage. The muzzle end of the barrel was closed off with a watertight tampion when not in use, and various methods of securing the breech where tried, from removable covers to screw type watertight breech mechanisms. The 3"/23 Mk 9 gun mentioned above partially retracted into a watertight tub that penetrated down into the submarine's interior. This was done in part to help protect the breech mechanism from corrosion when not in use.

WWI experience also showed that submarines may have to defend themselves in foreign ports or from air attack so the Navy began to equip boats with light machine guns like the Lewis and the Browning Automatic Rifle, and eventually the larger and more capable M2 .50 caliber heavy machine gun. A doctrinal shift that de-emphasized submarine anti-aircraft defense and the perceived lack of need for inport self defense during the interwar years lead to a pause in the employment of larger medium caliber automatic weapons. The opening of hostilities in 1941 quickly swept away any objections to further development and 20 mm Oerlikon-style weapons quickly made an appearance, supplemented later by hard hitting 40 mm Bofors-style automatic cannons. Late in WWII, twin 20 mm mounts made an appearance on some of the Balao and Tench-class fleet boats. The .50 caliber and 20 mm guns were not corrosion resistant and were generally dismounted and taken below or stowed in topside watertight lockers before the sub dived.

Drawing by Jim Christley, updated by David Johnston.

Drawing by Jim Christley, updated by David Johnston.

The sub-optimal 3"/23 Mk 9 caused the Navy to quickly move on to more advanced 3 inch deck gun models, with 50 caliber versions having a longer barrel that provided greater muzzle velocity and thus greater range and hitting power. The S-class of 1919 was equipped with a 4"/50 caliber weapon, and that proved to be a nice step up in hitting power. With the V-class boats of the interwar period, the new fleet submarine and cruiser roles designed into these boats required a greater surface firepower. 5 inch and even massive 6 inch guns equipped the V-1, V-4, and V-5 groups.

By the mid-1930s the tactical view of the use of guns by submarines had shifted. Largely driven by Captain Thomas C. Hart, the president of the Navy's General Board, emphasis on gun armament shifted back to smaller caliber guns, over unwarranted fears that a large gun would prompt "foolhardy" submarine captains into an unwise surface encounter with the enemy. The new fleet submarines of the Porpoise, Salmon/Sargo, and Tambor/Gar-classes were all equipped with 3"/50 caliber weapons, over the objections of the submarine captains. As a compromise, Hart agreed to equip these boats with a foundation strong enough to handle a large 5 inch weapon. This proved to be a fortuitous decision when WWII started in 1941.

With the opening of hostilities the Submarine Service quickly moved to upgun the force. Many of the fleet submarines shifted to the well-liked 4"/50 Mk 12 weapon, with six of the Tambor/Gar boats getting a powerful but somewhat unwieldy 5"/51 caliber Mk 18 gun. A shifting of the war situation in mid 1944 lead some of the pigboat era fleet submarines to receive the 5"/25 caliber Mk 40 gun, an excellent compromise between hitting power and usability. Even the old S-class boats had their topside armament shifted, losing the 4"/50s and receiving a 3"/50 instead, but upgunned with 20 mm auto cannons.

The rapidly changing tactical and strategic situation after the end of WWII with an emphasis on submerged endurance and speed caused the Submarine Service to quickly abandon the use of deck guns on submarines. A forty year period of submarine gunnery had come to an end, never to return.

Table Notes

The tables below list the major weapons used by the Submarine Service during the pigboat era. It will stray into WWII, as many of the fleet boats built and operated during the pigboat era served to the end of the war. Not every weapon is included; as stated above revolvers, pistols, and rifles are not listed due to a large number of variants and the inability to precisely state which variant, if any, was used by submarine crews. The bulk of the data in the tables and the connected pages come from the following sources:

•Navweaps.com
•U.S. Submarine Deck Guns, Jim Christley, 2010
•US Submarines 1900-35, Jim Christley, 2011
•U.S. Submarines through 1945, Norman Friedman, 1995
•The Fleet Submarine in the U.S. Navy, John D. Alden, 1979
•Leeward Publications Ship's Data 5, USS Bowfin (SS287), Arnold S. Lott & Robert F. Sumrall, 1975

In addition the authors have done an extensive amount of photographic research that backs up the observations in the references and our narrative above.

All measurements will be in the Imperial system unless otherwise noted (i.e. 20 mm). In the tables below the Photos & More Info column will provide a link to a follow on pages that expands on the information in the tables.

Three notes about frequently confused terms:

1. Caliber - This term has two definitions and describes both the diameter of the gun's bore in inches or millimeters, and on larger guns it is used to describe the length of the barrel. In the second use a 3"/50 caliber gun would have a barrel length of 50 times the guns' bore size, i.e. 150 inches.
2. Mark and Mod - Deck gun and their mounts will have an official designation, i.e. Mark (Mk) 12. Subsequent modifications to the mount will have a Modification (Mod) number in addition to the Mk number, such as Mk 12 Mod 6. A gun designated as a Mk 12 Mod 0 will be the original version of the gun mount.
3. Gun vs. gun mount - The U.S. Navy employs a somewhat confusing designation system when it comes to guns. A complete gun system will consist of both the gun itself, and the mount, the support structure under the gun that is attached to the deck and allows the gun to both elevate and train left or right. As an example a 4"/50 caliber Mk 12 Mod 11 gun mount consists of a Mark 9 gun attached to its Mk 12 mount. This is done so that different guns can be used with the same mount. Pigboats.COM will always use the designation for the gun mount, since it refers to the complete weapon system. Admittedly, this murky issue has even confused the webmasters in the past, so we have started an effort to correct this issue on our other pages.

Please contact us at the email listed below if you have any additions or corrections to the information presented here.

Machine Guns

Designation	Type	Manufacturer	Cartridge	Capacity/Feed Type	Action	Weight (lbs)	Length OA (in)	Rate of Fire (RPM)	Muzzle Velocity (Ft/s)	Effective Range (yds)	Dates of Use	Photos & More Info
M1917 Lewis Machine Gun	Light Machine Gun	Savage Arms	.30-06 Springfield	47/pan magazine	Gas, rotating open bolt	28	50.5	600-800	2440	880	1917-1945	Lewis Gun
M1918 Browning Automatic Rifle	Light Machine Gun	Colt/Winchester	.30-06 Springfield	20/detachable box magazine	Gas, rising bolt lock	15.98	47	500-650	2822	100-1500	1918-1945	B.A.R.

Deck Guns

Mount Mark/Mod	Bore Size/Caliber	Weight w/mount (lbs)	Length OA (in)	Elevation (deg)	Range at elevation	Muzzle Velocity (fps)	Rate of Fire (RPM)	Ammo type/weight complete (lbs)	Bursting Charge for Common Type (lbs)	Subs used on/Dates of service	Photos & More Info
Mk 9	3"/23	~1000	77.05	-15 to +65	5000@9.47	1650	8-9	Fixed/16.5	.28	L, M, O, S-1	3"/23 Mk 9
Mk 7 Mod 19	3"/50	5400	164	-20 to +30	4500@4.3	2700	15-20	Fixed/24	1.27	R, Porpoise-class	3"/50 Mk 17 Mod 19

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