155 mm caliber

155 mm (6.1 in) is a common, NATO-standard, artillery caliber. It is defined in AOP-29 part 1 with reference to STANAG 4425. It is commonly used in field guns, howitzers, and gun-howitzers.

Land warfare

The caliber originated in France after its defeat in the Franco-Prussian War of 1870-1871, when an artillery committee met on 2 February 1874 to discuss new models for the French fortress and siege artillery, among which there was a piece in the 14 to 16 cm caliber range (later became De Bange 155 mm cannon). After several meetings, on 16 April 1874 the committee settled on the 15.5 cm caliber (in the subsequent program-letter of the committee, dating from 21 April 1874, the caliber was for the first time expressed as 155 mm).

Since the early 21st century, most NATO armies have adopted 155 mm weapons as an all-purpose standard. They are seen as striking a good compromise between range and destructive power, while using only a single caliber simplifies logistics. This has led to the obsolescence of larger caliber artillery weapons such as the 175 mm (6.9 in) and 203 mm (8 in), although some militaries retain 105 mm (4.1 in) weapons for their light weight and portability. Russian guns and those of former Soviet bloc countries tend to use 122 mm (4.8 in), 130 mm (5.1 in) and 152 mm (6.0 in) weapons in similar roles.

Naval warfare

Since the end of WWII, 155 mm has not found any use among naval forces despite its ubiquity on land, with most NATO and aligned navies using 76 mm (3 in), 100 mm (3.9 in), 114 mm (4.5 in), or 127 mm (5 in) guns on modern warships. At one point the British Ministry of Defence studied "up-gunning" the Royal Navy's 4.5 inch Mark 8 naval guns to give increased firepower and a common caliber between the Royal Navy and the British Army. However, despite superficially appearing to be inferior based on a simple comparison of round diameters, when firing conventional ammunition the smaller, 4.5 in, naval gun is comparable to the standard 155 mm gun-howitzer of the British Army. The standard shell from a 4.5 in naval gun has the same, if not better, range. Only by using rocket-assisted projectiles (RAPs) can most 155 mm guns have comparable range to the 4.5 in naval gun and by doing so there is a reduction in the payload. This is because naval guns can be built much more strongly than land-based self-propelled gun-howitzers, and have much longer barrels in relation to caliber (for example the Mark 8 has a barrel length of 55 calibers, while the standard AS-90 self-propelled gun has a barrel length of 39 calibers). This allows naval guns to fire heavier shells in comparison to shell diameter and to use larger propellant charges in relation to shell weight leading to greater projectile velocities. In addition, even without active cooling, the heavier naval gun barrels allow a faster sustained rate of fire than field guns, and this is exploited with an autoloading system with a capacity of several hundred rounds. The 155 mm is better than the 4.5 in naval gun for firing cannon-launched guided projectiles (CLGP) as the lower velocity of the 155 mm round makes it much easier for the projectiles' internal electronic guidance systems to survive being fired.

While the US Navy's Advanced Gun System (AGS) also uses a 155 mm caliber, it is not compatible with NATO-standard 155 mm ammunition. However, only one type of ammunition was ever developed, and procurement was discontinued in 2016 due to its high cost, making the AGS unusable.^[1]