Description

Used as secondary guns on the last US pre-dreadnought classes. This caliber was selected as it was considered to be the largest possible given the technology of the time that was suitable for a rapid-fire (RF) secondary gun.

Many guns removed from old battleships were used as mobile land artillery (tractor mountings) during World War I. The mountings were designed by BuOrd and built by the Baldwin Locomotive Works in Philadelphia, Pennsylvania. The US Marines ordered 20 of these guns and the Army ordered 34 guns. 18 guns were delivered to the Marines and 20 to the Army prior to the Armistice, but none of these were actually used in France. One of the tractor mountings still exists and has been restored, as can be seen on the additional pictures page. An additional number of guns, still in their naval pedestal mountings, were used as railway guns during World War I.

During World War II, a number of the surviving guns were used in emergency coastal defense batteries. Two of the coastal guns still exist at Ft. Derussy at Pearl Harbor, Hawaii and as of 2006, four more were mounted at Bora Bora, French Polynesia.

In 1908 AP projectiles were fitted with a longer ballistic cap of 7crh which improved their penetration ability at longer ranges.

Mark 1 was for serial number 1 gun and was constructed of liner, tube, jacket, three hoops and a locking ring. It had a screw-box liner and was hooped from breech to 47.5 inches (120.65 cm) from the muzzle. Equipped with an experimental Welin breech block and uniform rifling 1/25. Mark 2 was of similar construction but was hooped all the way to the muzzle and had increasing rifling 0 to 1/25. It was also one caliber or some 7" (17.8 cm) longer than the Mark 1. Mark 2 Mod 1 had a conical nickel-steel liner. There were also two experimental Mark 2 guns, serial numbers 2 and 3, which had wider diameter breech ends. Gun S/N 2 was modified to become the Mark 2 Mod 2 by giving it a conical nickel-steel liner and a modified breech mechanism.

Gun Characteristics

Designation 7"/44 (17.8 cm) Mark 1
7"/45 (17.8 cm) Mark 2
Ship Class Used On Connecticut (B-18) and Mississippi (B-23) Classes
Date Of Design about 1900
Date In Service 1906
Gun Weight 12.8 tons (13.0 mt)
Gun Length oa Mark 1: 316.0 in (8.026 m)
Mark 2: 323.0 in (8.204 m)
Bore Length Mark 1: 308 in (7.823 m)
Mark 2: 315 in (8.001 m)
Rifling Length N/A
Grooves N/A
Lands N/A
Twist Mark 1: Uniform RH 1 in 25
Mark 2: Increasing RH 0 to 1 in 25
Chamber Volume N/A
Rate Of Fire 4 rounds per minute

Ammunition

Type Bag
Projectile Types and Weights
(see Notes 1 and 2)
AP Mark 6 Mods 0 and 1 - 165 lbs. (74.8 kg)
AP Mark 10 Mod 2 - 165 lbs. (74.8 kg)
AP Mark 12 Mods 1 and 2 - 165 lbs. (74.8 kg)
Common - 165 lbs. (74.8 kg)

Field Mark 13 Mods 1 and 2 - 152 lbs. (68.9 kg)
Bombardment Mark 14 Mod 2 - 153.8 lbs. (69.8 kg)

Bursting Charge AP Mark 6 - 4.31 lbs. (2.0 kg) Explosive D
AP Mark 10 - 4.31 lbs. (2.0 kg) Explosive D
AP Mark 12 Mod 1 - 4.0 lbs. (1.8 kg) Explosive D
AP Mark 12 Mod 2 - 3.5 lbs. (1.6 kg) Explosive D
Common - 5.5 lbs. (2.5 kg) Explosive D

Field Mark 13 - 24 lbs. (10.9 kg) Cast TNT
Bombardment Mark 14 - 24 lbs. (10.9 kg) Cast TNT

Projectile Length AP Mark 6 - 23.64 in (60.0 cm)
AP Mark 10 - 23.73 in (60.3 cm)
AP Mark 12 - 23.68 in (60.1 cm)
Common - about 23.64 in (60.0 cm)

Field Mark 13 - 29.58 in (75.1 cm)
Bombardment Mark 14 - 28.84 in (73.3 cm)

Propellant Charge 58 lbs. (26.3 kg) SPD
Muzzle Velocity 2,700 fps (823 mps)
Working Pressure 17.0 tons/in2 (2,680 kg/cm2)
Approximate Barrel Life N/A
Ammunition stowage per gun Connecticut class: 100 rounds
Mississippi class: 111 rounds
  1. All AP projectiles had almost identical nose shapes, but the designs were very different. AP Mark 6 had no ballistic cap, but the AP cap was essentially shaped like a thick-walled ballistic cap. AP Mark 10 had a ballistic cap covering a flat-nosed AP cap. AP Mark 12 had a ballistic cap covering a concave AP cap. See sketch at the "additional pictures" link above.
  2. Field and Bombardment rounds were developed for Marine and Army artillery units, they were not used on ships. These had similar projectile shapes, but the Field round did not have a base fuze.
  3. Bourrelet diameter for AP Mark 6 was 6.990 inches (17.8 cm). All other rounds had a bourrelet diameter of 6.985 inches (17.7 cm).

Range

Range AP Shell
Elevation Distance Striking Velocity Angle of Fall
3.0 degrees 6,000 yards (5,490 m) 1,810 fps (552 mps) 3.9
4.1 degrees 7,500 yards (6,860 m) 1,635 fps (498 mps) 5.7
15 degrees 16,500 yards (15,090 m) --- ---

Time of flight for MV = 2,700 fps (823 mps)
   6,000 yards (5,490 m): 8.2 seconds
   7,500 yards (6,860 m): 10.8 seconds

Armor Penetration with AP Shell

Range Side Armor Deck Armor
0 yards (0 m) 9.60" (244 mm) ---
6,000 yards 5.21" (132 mm) ---
9,000 yards 3.84" (98 mm) ---
12,000 yards 3.43" (87 mm) ---

This data is for face-hardened Harvey plates from "Ordnance Data Sheets" of 1905 and is for the older shell design.

Range Side Armor Deck Armor
6,000 yards (5,490 m) 6.3" (160 mm) ---
9,000 yards (8,230 m) 4.3" (109 mm) ---
12,000 yards (10,920 m) 3.2" (81 mm) ---

This data is from "Elements of US Naval Guns" of 1918 and is for the 7crh projectile at a muzzle velocity of 2,400 fps (732 mps). Data is corrected for angle of fall and may also refer to harder armor than used for the 1905 data.

Mount/Turret Data

Designation Single pedestal type for casemates
   Connecticut (12) and Mississippi (8): Mark 1 and Mark 2
Weight 25 tons (26 mt)
Elevation -7 / +15 degrees
Elevation Rate N/A
Train about +150 / -150 degrees
Train Rate N/A
Gun recoil Nominal: 19 in (48 cm)
Maximum: 21 in (53 cm)
Loading angle Any angle
  1. The World War I tractor mounting allowed a maximum elevation of 40 degrees. At this angle, a maximum range of about 24,000 yards (21,900 m) could be achieved.
  2. The railway units used the Mark 2 Mod 3 naval mounting together with a special adapter casting, which both mated the gun pedestal to the railway car and raised the gun muzzle to a safe clearance height above the car. The casting weighed about 13,000 lbs. (5,900 kg). This mounting allowed a full 360 degrees of traverse. The railroad car itself was a drop-frame type that needed to be lowered to the rails and its four outriggers set up before the gun could be fired. See photograph below.

Additional Pictures

Sources

"Naval Weapons of World War Two" by John Campbell
"US Naval Weapons," "US Cruisers: An Illustrated Design History" and "US Battleships: An Illustrated Design History" all by Norman Friedman
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"The Engineer" 27 April 1917 as quoted in Warship International No. 1, 1994
USNI Proceedings Vol. 45, No. 7, July 1919
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"Naval Ordnance - A Text Book" revised in 1915 by Lt. Cmdr. Roland I. Curtain and Lt. Cmdr. Thomas L. Johnson
"U.S. Explosive Ordnance: Ordnance Pamphlet 1664 - May 1947" by Department of the Navy
"Range and Ballistic Tables 1935" by U.S. Department of Ordnance and Gunnery
"Handbook of Ordnance Data No. 1861, 15 November 1918" by United States Army Ordnance Department
"United States Naval Guns: Their Marks and Modifications" Ordnance Pamphlet No. 127, December 1916, Revised January 1918
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Gene Slover's Navy Pages
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Special help from Charley Seavey

Off-site Resources

Interesting datapage on the tractor mounts:
Track-propelled Gun Mk.2 1918

Page History

15 August 2008 - Benchmark
29 March 2009 - Fixed typographical error
06 September 2009 - New pictures of mobile tractor mounting
16 October 2010 -
16 October 2010 - Modified off-site Resources and added picture of railway mounting
21 July 2012 - Added a mention and photographs of Bora Bora guns
15 May 2015 - Redid photograph of USS Vermont and fixed link to Track-propelled Gun
28 December 2015 - Updated caption
30 July 2016 - Converted to HTML 5 format