Newton 6-inch Mortar

The Newton 6 inch Mortar was the standard British medium mortar in World War I from early 1917 onwards.

Description
The Newton 6 inch replaced the 2 inch Medium Mortar beginning in February 1917.

It was a simple smooth bore muzzle-loading (SBML) mortar consisting of a 57 in one-piece steel tube barrel, with a "striker stud" inside the centre of the closed base of the tube. The rounded external base of the tube sat in a socket in the flat cast steel base, which in turn sat on a wooden platform. An "elevating guy" (cable) connected to a loop in the upper side of the barrel and the rear end of the bed. "Traversing guys" (cables) connected to loops on each side of the barrel and eyebolts on the upper sides of the bed. Hence aiming of the barrel was done by adjusting the length of the guys via adjusting screws. A socket in the barrel base allowed for emergency firing via a "misfire plug" in the case of misfires (i.e. if the bomb remained in the barrel due to failure of the propellant to ignite).

Combat service
British Empire Divisions were initially equipped with 3 batteries of 4 mortars designated X, Y, Z. From February 1918 onwards these were consolidated into 2 batteries, X and Y, of 6 mortars each, and Z was dissolved. In British use they were operated by the Royal Field Artillery and formed part of the Divisional Artillery with 1 battery attached to each of the Divisional artillery brigades.

The United States Army began production and equipping with this mortar late in the war but it is doubtful whether any were used in combat. The mortar was operated from concealed pits close to the front line during trench warfare, and was used in the open during the final "mobile warfare" phase of the First World War, as demonstrated in the photograph, depending on available transport. The disassembled weapon was usually transported on horsedrawn carts but the Canadian Automobile Machine Gun Brigade (the Canadian Independent Force or "Brutinel's Brigade") is known to have successfully used the mortar both mounted on motor trucks and dismounted in the closing months of the war.

The 52-pound cast-iron fin-stabilised high explosive bomb carried the percussion primer at the base in the intersection of the 4 vanes (fins), consisting of a specially loaded blank .303 rifle cartridge. The basic propellant charges were contained in 4 small white cambric bags each containing 1 oz of guncotton yarn. These were held in place in the 4 angles between the bomb's fins. For ranges less than 1000 yards 1 or more bags could be removed, as per range tables.

For ranges above 1000 yd, additional charges were loaded before the bomb, held in 2 white cambric bags each containing 1 oz 4 drm cordite.

In action the gunners would adjust the angle of the barrel via the elevating guy (for distance) and traversing guys (for direction). The manual warns: "See that the elevating and traversing screws of the guys are always tight. A slack guy leads to inaccurate shooting, and the stresses on firing are not equally distributed; this is usually the cause of the guys breaking".

The range tables specified the barrel angle and propellant charges required. The additional cordite propelling charge bags were dropped down the barrel if necessary, or necessary number of propellant charges removed from the bomb, and the bomb's fuze was set. The gunners stood back, the bomb was dropped down the barrel, the detonator in the base of the .303 cartridge in the base of the bomb struck a pin in the bottom of the barrel and fired, igniting the guncotton charges in the base of the bomb, which in turn ignited the cordite charges if present. The resulting rapid gas expansion propelled the bomb up the barrel and to its target.

1917 Range tables
52 lb Bomb, ML 6 inch Trench Mortar. Propellant : 1-4 one ounce guncotton charges in the base of the bomb, plus optional 2.5 oz cordite charge.

Weapons of comparable role, performance and era

 * Mortier de 58 mm type 2 : approximate French equivalent

Surviving examples

 * Army Memorial Museum, Waiouru, New Zealand
 * Royal Australian Artillery Museum, North Head, Sydney, Australia
 * Australian Army Infantry Museum, Singleton NSW Australia