The M-71 is a 155 mm 39 caliber towed howitzer manufactured by Israeli company Soltam Systems.
A deployed M-71
The Soltam M-71 in travel/towing configuration
155 mm is a NATO-standard artillery shell caliber that is used in many field guns, howitzers, and gun-howitzers. It is defined in AOP-29 part 1 with reference to STANAG 4425.
M107, M795, M483A1 155 mm projectiles
M107 projectile 155 mm projectile being loaded into an M777 howitzer