3-inch/70-caliber Mark 26 gun


The 3"/70 Mark 26 Gun was a US post war naval anti-aircraft gun. Developed as a joint project with the United Kingdom, which called it the QF 3-inch Mark N1 gun, it had a water-cooled barrel combined with an automatic loader to deliver high rates of fire.
The gun design was based on experience defending United States warships from Japanese kamikaze attacks in World War II and based on the [3-inch/50-caliber gun|3-inch/50 Caliber (artillery)|caliber gun]. The name indicates in US Navy terminology that this piece of naval artillery fires a projectile in diameter and has a barrel length of 70 calibers . "Mark 26" refers to the gun mounting rather than the gun itself.
Due to the long development period, the gun did not enter service until 1957 and the mounts proved problematic; the gun was removed from most US warships after a short service life, being fully retired by 1970.
The British mountings, known as Mark 6 in the Royal Navy, were to a different design and though also complex and subject to feed problems were more effective.

History

Development of the 3"/70 Mark 26 gun began from observations by the US Navy that the Oerlikon 20 mm cannon and the Bofors 40 mm anti-aircraft guns were too small to 'kill-stop' Japanese kamikaze aircraft. As a joint project between the United States and the United Kingdom, its design being finalized in 1956, the Mark 26 missed any wartime action. It was an essential improvement over the previous version, the 3-inch/50-caliber Marks 27, 33, and 34, increasing the barrel length by and improving range by over and elevation by 5 degrees. The 3-inch round was chosen because it was the smallest caliber ammunition that could be fitted with a VT radar proximity fuze. The twin barrel mount was believed to be more effective against faster aircraft and guided missiles than the single mounted 5"/54 caliber Mark 42 gun, hence, the single barrel version of the Mark 26 never saw service use.

Versions

The Mark 26 was the last of four versions of the 3"/50 caliber AA (anti-aircraft) artillery. The Mark 23 was the initial prototype on to test the fully automatic firing of the artillery. The next version was exactly the same despite an overall weight loss of the actual gun. The Mark 25's improvement was based on a rapid-fire horizontal-wedge breech. The final, and service ready, version incorporated all of these improvements as well as a water cooled monoblock system with a horizontally sliding breech mechanism.
The British mounting for the guns built by Vickers was the twin 3-inch/70 Mark 6. This was used on the British Tiger-class cruisers. The mounting could elevate to 90° at 30° per second and train at 60° per second.

Ammunition

USUK
TypeAA Mark 34 Mod 1HE Fuze NC101
Shell weight15 lbs.
Cartridge76.2 mm x 669R 76.2 mm x 662R
Propellant charge SPD
Overall weight36.2 lbs
Muzzle velocity
Barrel Lifeapprox 2,050 roundsN/A
Range19,500 yards at 45 degrees elevation19,500 yards at 45 degrees elevation
AA Ceiling38,000 feet 38,000 feet

The ammunition used in the Mark 26 is heavier than its earlier 3-inch rounds used by the US Navy. Although it was a joint project by the United States and the United Kingdom, the two countries used cartridges that differed slightly.
The UK also had a non-fragmenting round for practice and an inert training round.

Usage