M107 projectile

The M107 155mm projectile is the US Army and US Marine Corps' standard high explosive (HE) projectile for howitzers. It is a bursting round with fragmentation and blast effects.

The M107 is being superseded in the US military by the M795.

Development
The M107 is a development of the M102 155mm mm shell that was developed in the 1930s from the French Schneider 155 mm projectile for the Model 1917 Howitzer. The M107 differs from the M102 mainly in having a wider driving band.

The M102 shell was modified in 1944 to accommodate VT fuzes. This required a deeper fuze well. However, since most fuzes did not require such a deep cavity a small aluminium-wrapped 136 g TNT supplemental charge is fitted in the space.

Description
The body consists of a hollow steel shell containing high explosive (either TNT or Composition B) painted olive drab with yellow markings. A fuze adapter is screwed into the body and brazed in place. An eyebolt lifting plug is screwed into the fuze well to assist in transportation. The plug is removed and replaced with a fuze for firing. The complete projectile weighs 43.2 kg, is 800 mm long and contains 15.8% explosive by weight. It is a separate-loading projectile - propellant bags or MAC charges are loaded separately.

On detonation it produces approximately 1,950 fragments.

The M107 was approved for use in 1958 and issued to the army from 1959. Its intended replacement is the M795, manufacture of which began in 1999.

The M114 howitzer can fire an M107 up to 14.5 km using M4A2 "White Bag" propellant; maximum range is 18.1 km. Modified M107 rounds with base bleed and new aerodynamics can extend this range to around 32 km.

Despite relatively lackluster performance (Jane's describes it as having "an indifferent charge to weight ratio", "unsophisticated aerodynamic shape", "erratic fragmentation") compared to more modern high explosive rounds, it continues to be used by many countries, in particular in training exercises because of its low cost, high availability and smaller danger area than more modern designs. Its limited effectiveness also make it a useful option in peace support operations.

M107 is manufactured by several nations, sometimes with variations in the fill and or filling method, or other details, and is given a national designation. For example those produced to UK requirements are designated L21 not M107; German examples were designated DM21.

By the 1970s M107 was an out of date design and some European armies started replacing their war stocks with modern designs such as L15. However, M107 was retained for training because it was cheap and being less lethal had a smaller peacetime safety area, an important consideration given the small European training areas.

Specifications

 * Weight as fired: 43.88 kg
 * Explosive content:
 * Composition B: 6.985 kg plus 0.136 kg TNT supplemental charge.
 * TNT: 6.62 kg plus 0.136 kg TNT supplemental charge.
 * Length (excluding fuze): 605.3 mm
 * Body diameter: 154.89 mm
 * Driving band diameter: 157.98 mm
 * Fuzes (with supplemental charge):
 * PD M51A5, M728 family, M557, M572, M739, M564, M577, M582, M732
 * Fuzes (without supplemental charge):
 * M728
 * Manufacturer: American Ordnance LLC & Scranton Army Ammunition Plant