| Year | August 1941 |
| Vehicle Type | [@type] |
| Origin & Designer | [@designer] |
| Numbers Produced | 572 |
| Crew | 6 (Commander, two Gunners, Two Loaders & Driver) |
| Main Armament | 1 x 81mm M1 Mortar (Rear Facing) |
| Main Armament | [@sponson_traverse] |
| Elevation | -7° to +60° |
| Turret Traverse | 60° (Manual) |
| Gun Traverse | [@gun_traverse] |
| Gun Mount | [@gun_mounts] |
| Maximum Range | [@maximum_range] |
| Armour Penetration | [@armour_penetration] |
| Gun Sight | 6.10m |
| Secondary Armament | 1 x .30 cal M1919A4 Machine Gun |
| Smoke Discharger | [@smoke_discharger] |
| Ammunition Carried | 112 x 81mm + 2000 x .30 cal |
| Height | 2.27m |
| Width | 1.96m |
| Length | 6.10m |
| Combat Weight | 7.970 kg |
| Ground Clearance | 0.28m |
| Fording Depth | 0.81m |
| Trench Crossing | 0.76m |
| Obstacle Clearance | 0.30m |
| Climbing Ability | 31° |
| Radio | [@radio] |
| Armour | Upper Hull Front: 13mm. Lower Hull Front: 6.4mm. Upper Hull Sides: 6.4mm. Lower Hull Sides: 6.4mm. Hull Rear: 6.4mm. Hull Top: Open. Hull Bottom: 6.4mm. Hood: 6.4mm. |
| Engine | White 160AX 147 (Petrol) |
| Transmission | 4 Forward & 1 Reverse |
| Maximum Road Range | 198 miles (320 km) |
| Maximum Cross Country Range | 175 miles (282 km) |
| Maximum Water Range | [@maximum_water_range] |
| Maximum Road Speed | 45 mph (72 kph) |
| Maximum Cross Country Speed | 9 mph (15 kph) |
| Maximum Water Speed | [@maximum_water_speed] |
| Variants | M4A1 MMC: Quantity: 600 Year: May 1943 New reinforced Floor to allow for vehicle firing M21 MMC: Quantity: 110 Year: January 1944 |
| Notes | Based on the half-track car M2 and built by White, the M4 carried a rear facing 81mm mortar, the mortar also carried a base plate for ground firing, as the weapons was only designed to fire from the vehicle in an emergency. This was changed with the M4A1 which added a strengthened hull to accommodate firing the weapon from the vehicle The M21 was based on the M3 and had a forward facing 81mm mortar. This allowed for easier firing and to maneuver the vehicle to a new position. The M21 was also built by White with 110 built between January and March 1944 before production was stopped. |