The Major Caliber Light Weight Gun (MCLWG) program was an ambitious attempt at solving these problems. The goal of this program was to produce a larger-caliber gun capable of supporting amphibious landings yet still light enough to fit even on destroyer-size ships. The weapon was originally intended to be an adaptation of the Army's 175 mm (6.9") artillery gun, but the 8" (20.3 cm) caliber was selected during the initial evaluation testing in the early 1970's. The projectiles planned for the new weapon were to combine a large explosive charge together with long range and high accuracy through laser guidance and thus were to be able to attack even small targets such as individual bunkers. To make this weapon widely available throughout the fleet, plans were made to mount it on many of the proposed DX, DXG and CSGN designs of the 1970s, but the only ships actually designed and built to use it were the Spruance (DD-963) class destroyers (see Mount / Turret Notes below for details).
Although the prototype was successful, the program was cancelled in 1978 as a result of budget considerations during the defense cutbacks of the late 1970s.
The chamber of this weapon was designed to be able to handle a 10-11 caliber projectile. One of the proposed munitions was an extended range guided round that would have been around 90 inches (229 cm) long.
As the USN test ship for this weapon from 1975 to 1979, the USS Hull (DD-945) was the only destroyer ever to mount an 8" (20.3 cm) cannon. The mount was removed from the USS Hull in 1979 and is now at the Naval Surface Warfare Center in Dahlgren, Virginia.
The gun barrel for the Mark 71 was the Mark 28 Mod 1, a 55 caliber two-piece loose liner barrel. The production gun mount was to have used a one piece monobloc barrel designated the Mark 32.
8"/55 (20.3 cm) Mark 71 on USS Hull DD-945
|Designation||8"/55 (20.3 cm) Mark 71 (Mounting)
8"/55 (20.3 cm) Mark 28 and Mark 32 (Guns)
|Ship Class Used On||Prototype on USS Hull (DD-945)
Planned for Spruance (DD-963) and Strike Cruiser (CGSN) classes
Planned for Long Beach (CGN-9) as a rebuilt Aegis Cruiser
|Date Of Design||1971|
|Date In Service||1975|
|Gun Weight||19,860 lbs. (9,008.5 kg)|
|Gun Length oa||N/A|
|Bore Length||440 in (11.176 m)|
|Rifling Length||382 in (9.703 m)|
(see Note 1)
|Mark 28: Uniform RH 1 in 25
Mark 32: Uniform RH 1 in 20
|Chamber Volume||3,123 in3 (51.19 dm3)|
|Rate Of Fire
(see Note 2)
|12 rounds per minute|
1) A one in twenty twist was required for the new design projectiles (see below) to be stable in flight, which accounts for the twist difference between the prototype and the production barrels.
2) During test firings in 1973 the sustained rate of fire was determined to be 11.7 to 12.6 rounds per minute.
3) The gun blast profile for this gun was established as being slightly less severe than that for an 8-inch bag gun.
|Projectile Types and Weights
|HC Mark 25 - 260 lbs. (117.8 kg)
New design projectiles: 240 lbs. (108.9 kg)
|Bursting Charge||HC - 21.3 lbs. (9.7 kg)
New design: N/A
|Projectile Length||HC Mark 25: 32 in (81.3 cm)
New design: 44 in (111.8 cm)
|Propellant Charge||83 lbs. (37.65 kg) NC|
|Muzzle Velocity||HC Mark 25: 2,650 fps (808 mps)
New design: 2,950 fps (899 mps)
|Working Pressure||24.6 tons/in2 (3,770 kg/cm2)|
|Approximate Barrel Life||N/A|
|Ammunition stowage per gun
(see Notes 3, 4 and 5)
|75 rounds of ready ammunition on mount|
1) The baseline shape of the new projectiles was 5.5 calibers in length with a one caliber boattail and had a discarding rotating band. These projectiles were not completed at the time of the cancellation of the Mark 71 program.
2) In addition to the rounds listed above, there was also a Paveway or CLGP guided round. This round had a special ramming sheath which was a modified cartridge case that supported the projectile, protected the fin assembly and provided a standard interface for the handing system. Loading and firing of this round did require a double operation due to its longer length.
3) Ready service rounds were carried in a single drum containing 75 complete rounds.
4) The Mark 71 installation on USS Hull was restricted to the ready service magazine as no additional hull volume could be spared for further magazine capacity. One version of the CSGN shows a magazine capacity of 400 rounds in addition to the ready service rounds.
5) The planned ammunition stowage for the Spruance class (DD-963) was as follows:
The first platform magazine (Fr. 77-94) held 129 ballistic projectiles, 119 standard propellant charges and 32 reduced charges.
|Elevation||With 260 lbs. ( 117.8 kg) Mark 25 HC|
|Range @ 41 degrees||32,000 yards (29,260 m)|
|Over the years, I have heard many tales
of how USS Hull suffered severe frame and plate cracking as a result of
firing the Mark 71. I asked my friend Leo Fischer, a project engineer
on the Mark 71, for his view of the matter. The following is his
There have been many stories over the years about cracks in the structure of the USS Hull resulting from firing the Mark 71. Most of these I would classify as "urban legends."
|USS Hull made a number of test shoots
in June 1976. The following excerpt on those tests is from "Major
Caliber Lightweight Gun Integrated Development Plan, February 1978."
CNO Project 186, consisting of ten Eight-Inch Unpowered SAL Guided Projectile firing tests from the USS Hull (DD-945) Mk 71 Major Caliber GP's (as well as 24 nonguided rounds, consisting of nine Ballistic Shapes and fifteen conventional rounds) were fired against shore and seaborne targets. Two GP's were fired at a bunker target (MULE Laser - 13 KYD firing range), two at a stationary truck (MULE Laser - 13 KYD firing range), one at a moving tank (Spot Laser - 16 KYD firing range), and five at an ex-destroyer target HULK (13 to 16 KYD firing ranges).SAL (short for SAL-GP) stands for Semi-Active Laser, GP = Guided Projectile (Paveway). KYD = 1,000 of yards (about 900 m). MULE = AN/PAQ-3 Modular Universal Laser Equipment which was a man-portable, target-designating laser. All five Paveway GP rounds fired at the destroyer hit the target. Comments Leo Fischer:
The five hits on the target destroyer were with the 8-inch Paveway GP. Actually, we were not supposed to sink the target, but the laser spot on the hull reflected down onto the water and one of the rounds hit low and put a hole below the water line, which meant that we were stuck with a slowly flooding target. We had to pump about 50 rounds of 5-inch into the target before it finally sank.The ex-destroyer refered to in this report was USS Burns DD-588. For information on the wreck of USS Burns, please see this link.
(see Note 1)
|172,895 lbs. (78,425 kg) (including ready ammunition)|
|Elevation||-5 / +65 degrees|
|Elevation Rate||20 degrees per second|
|Train||about +160 / -160 degrees|
|Train Rate||30 degrees per second|
|Gun recoil||36 in (91.44 cm)|
1) The weight given above is only for the rotating gunhouse. Not including ammunition, total weight was 224,471 lbs. (101,819 kg) including 32,611 lbs. (14,792 kg) below decks.
2) Standard manning was six enlisted men.
3) This weapon requires a stronger supporting foundation than that for the 5"/54 (12.7 cm) Mark 45 in order to accommodate the increased recoil forces. Only the bow position on the Spruance class was strengthened to take this weapon, the stern position was not modified to support the larger gun. As far as I have been able to determine, all Spruances were completed with the strengthened bow foundation.
4) Some of the early design alternatives for the DXG development program of the 1970s show a Mark 71 on the bow. After the Mark 71 was cancelled in 1978, all new design alternatives for what ultimately became the Ticonderoga CG-47 class showed a 5"/54 (12.7 cm) Mark 45 in the bow position. Like the Spruance class from which it was developed, the stern position for the Ticonderoga class was always planned for the Mark 45.
5) When Long Beach (CGN-9) was being considered for conversion to an Aegis cruiser during the 1970s, at least one proposal shows her with Mark 71 mountings on the bow and stern.
6) Plans for the canceled Strike Cruiser (CSGN) show one Mark 71 on the bow.
7) A study performed in 1991 by Gibbs and Cox showed that it was technically feasible to install a Mark 71 on a DDG-51 Flight I variant; however, the installation had some serious drawbacks. The height of the required barbette caused the mount to restrict the view of the bow from the bridge. This was considered to pose a safety issue when maneuvering the ship in congested waters. In addition, the height of the mount would have imposed severe restrictions on the use of the forward VERTREP station. This plus the cost and the small magazine size - 204 8-inch (20.3 cm) projectiles vs. 600 5-inch (12.7 cm) projectiles - caused the installation to be deemed undesirable.
01 April 2008 - Benchmark
11 January 2011 - Added ammunition stowage details, comments about cracks on USS Hull, CLGP ramming sheath, note about DDG-51 variant
05 March 2011 - Added USS Hull test shoot data