SOLDIER officer 81 wrote:
Thats a great model Seasick. I wish I could find that old discussion about the Mk 71.
This one?
History
After the retirement of the last of the World War II Baltimore and Cleveland class cruisers in the 1970s, the only ship-based shore-bombardment weapon remaining in the USN was the 5"/54 (12.7 cm) gun. This weapon was out-ranged by existing Soviet coast defense guns and its projectiles were incapable of destroying hardened bunkers. With the Navy's concentration on carrier task forces, it was also apparent that there would not be any future surface-warfare ships large enough to carry multiple heavy weapons. These developments were quite worrisome to those planners charged with ensuring the success of amphibious assaults.
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 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 all Spruance (DD-963) class destroyers and Ticonderoga Aegis (CG-47) class cruisers.
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.
Mount
Single Mount: Mark 71
Weight (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)
Notes:
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.
Gun
Designation
8"/55 (20.3 cm) Mark 71 (Mounting)
8"/55 (20.3 cm) Mark 28 and Mark 32 (Guns)
Ship Class Used On USS Hull DD-945
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)
Grooves N/A
Lands N/A
Twist (see Note) 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 12 rounds per minute
Note: 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.
Ammunition
Type Separate
Projectile Types & Weights: HC Mark 25 - 260 lbs. (117.8 kg), New design - 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 75 rounds of ready ammunition on mount
Notes:
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.
Range
Elevation With 260 lbs. ( 117.8 kg) Mark 25 HC
@ 41 degrees 32,000 yards (29,260 m)
