6"/40 caliber gun

6"/40 caliber Mark 4
U.S.S. Massachusetts, 6 inch gun and crew USS Massachusetts (BB-2), 6-inch/40 caliber gun and crew.
Type	Naval gun
Place of origin	United States
Service history
In service	1885
Used by	United States Navy
Wars	World War I
Production history
Designer	Bureau of Ordnance
Designed	1883
Manufacturer	U.S. Naval Gun Factory
Produced	1896 – 1905
Number built	72
Variants	Mark 4 Mod 0 – Mod 13 (no Mod 6)
Specifications
Weight	13,370 lb (6,060 kg) (without breech)
Length	256.1 in (6.50 m)
Barrel length	243.8 in (6.19 m) bore (40 calibers)
Shell	105 lb (48 kg) naval armor-piercing
Caliber
Traverse	−150° to +150°
Rate of fire	As commissioned: 1.5 rounds per minute After 1906: 7.6 rounds per minute
Muzzle velocity	2,150 ft/s (660 m/s)
Effective firing range	9,000-yard (8,230 m) at 15.3° elevation 18,000-yard (16,459 m) at 30.2° elevation

The 6"/40 caliber gun Mark 4 (spoken "six-inch-thirty-caliber") were used for the secondary batteries of the United States Navy's Indiana-class and Illinois-class battleships. They were also used as the primary battery on the Cincinnati-class protected cruisers.

Design

The 6-inch/30 caliber Mark 4 guns were developed before the Spanish-American War and still used black powder or brown powder, in later years they were not considered strong enough to withstand the higher chamber pressures generated by the newer smokeless powder adopted around 1898. Many were obsolete before the start of World War I, namely the Mods 0, 1, 2, 3, and 8, and were removed from service, however, since they were stronger than the earlier Mark 1, 2, and 3's, 45 of them were still in active service June 1917.

The first Mark 4, gun No. 133, was completed July 1896. Production numbers were Nos. 133 – 196, 260 – 263, and 423 – 426. It was the first 6-inch Navy gun designed from the beginning to use case, semi-fixed, ammunition. The gun was constructed of gun steel using a tube, jacket, and seven hoops. It was originally threaded to be mounted in the Mark 5 gun mount. Mod 0 was very similar to the Mark 3 Mod 2 but with the breech ring lengthened 0.1 in (3 mm), the trunnion hoop removed and the barrel threaded.

Mod 1, No. 155, was of similar construction, but was 0.31 in (8 mm) longer, only 4 hoops, and an experimental breech mechanism. The chamber volume was also increased slightly from 1,320 cubic inches (21,600 cm³) to 1,367 cubic inches (22,400 cm³). Mod 2, for Mark 6, 7, and 9 gun mounts, was similar but with 1.8 in (46 mm) cut off the breech end of the gun. Only one gun, No. 136, was modified in this way. Mod 3 was similar in construction to the Mod 1 but with its mounting threads located differently and it also had a threaded bronze sleeve. Mod 4 only differed from Mod 1 construction in adding a shoulder for a mounting yoke and with a different location for the mounting threads. The chamber volume was reduced slightly to 1,355 cubic inches (22,200 cm³). Mod 5 only differed from Mod 4 in adding a muzzle bell. Mod 6 was skipped and Mod 7 was an experimental Mod 4 bored out to use bag ammunition, a 1,367 cubic inches (22,400 cm³) chamber, 1.83 inches (46 mm) think faceplate added to the breech end, and a trunnion hoop added. With Mod 8, gun No. 161, a Mod 4 gun, a 30 inches (760 mm) muzzle liner and muzzle bell were used and the rifling was a uniform 1/25 instead of 0 to 1/35. Mod 9 was a Mod 4 using a tube constructed of nickel-steel instead of the normal gun-metal and again the rifling was a uniform 1/25. Mod 10 used a Mod 4 had a two-step cylindrical nickel-steel liner with the rifling changed to 0 to 1/25. Mod 11 used a Mod 4 but with only a one-step cylindrical nickel-steel liner and with a uniform 1/25 rifling. Mod 12 also used a Mod 4 with a nickel-steel liner and a 0 to 1/25 increasing twist rifling. The last Mod, Mod 13 consisted of a Mod 5 with a nickel-steel liner and the using an increasing twist rifling of 0 to 1/25.

Naval Service

Ship	Gun Installed	Gun Mount
USS Indiana (BB-1)	Mark 4: 6"/40 caliber	Mark 5: 4 × central-pivot
USS Massachusetts (BB-2)	Mark 4: 6"/40 caliber	Mark 5: 4 × central-pivot
USS Oregon (BB-3)	Mark 4: 6"/40 caliber	Mark 5: 4 × central-pivot
USS Illinois (BB-7)	Mark 4: 6"/40 caliber	Mark 4: 14 × pedestal mount Mark 7: 14 × pedestal mount (refit by 1905)
USS Alabama (BB-8)	Mark 4: 6"/40 caliber	Mark 4: 14 × pedestal mount Mark 7: 14 × pedestal mount (refit by 1905)
USS Wisconsin (BB-9)	Mark 4: 6"/40 caliber	Mark 6: 14 × pedestal mount Mark 7: 14 × pedestal mount (refit by 1905)
USS Cincinnati (C-7)	Mark 4: 6"/40 caliber	Mark 6: 1 × pedestal mount
USS Raleigh (C-8)	Mark 3: 6"/40 caliber	Mark 6: 1 × pedestal mount

External links

• Bluejackets Manual, 1917, 4th revision: US Navy 14-inch Mark 1 gun