Submarine Guns

Submarine Guns 1900-1941

For the first 14-15 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 L-class of 1914, and even then it was a retrofitted as the gun was not ready when the first boats were built. 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 the idea did not catch on in the USN for several more years.

It is likely that submarines from the C-class and 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 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 issued 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.

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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Ric Hedman & David Johnston
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