Easily portable and simple to operate, the mortar was ideally suited to the terrain of South Vietnam and the tactics of the NVA and, in particular, the Viet Cong. Ever conscious of US firepower, a well trained mortar team could set up a mortar position out of the sight of the enemy, loose off a number of rounds at maximum range and, due to the mortar rounds long flight time, be moving away from the firing site before the first rounds impacted on the target. Such maneuverability severely restricted allied counter-mortar fire or retaliation by air.
The mortar was particularly suited for attacking standoff targets such as US firebases or installations where its greater accuracy over the rocket allowed it to be used against point targets.
The VC and NVA deployed a wide variety of mortars, ranging in size from the small 50mm to the breech-loaded 160mm. However, the most common types were: the light Chicom Type 63 60mm mortar, Soviet M1937 and M1943 82mm mortars and the Soviet M1938 and M1943 120mm mortars.
NVA mortar positions were often cynically sited near to inhabited areas in order that the crew could seek refuge from air attack after firing a few rounds. The mortar position itself was generally a hole approximately 1.7-meters deep and 2-meters in diameter, invariably excellently camouflaged, with only the mortar tube fire path uncovered during firing. These mortars were frequently sited to fire along the long axis of the target in order to take advantage of the their small deflection error.
The lightweight 60mm mortar, weighing only 45-lbs when assembled for firing, was an ideal standoff weapon. The crew could fire it, then pick it up and move with it. With a maximum range of nearly two kilometers and a minimum range of only 90-meters, it also made for an excellent infantry support weapon.
LIGHT MORTARS: 60mm mortar (CHICOM Type 31 and Type 63, Soviet M40 series)
The Type 31 was a copy of the American M2 60 mm, and both were modelled on the French Stokes-Brandt M1935. These mortars had a square baseplate with a spade underneath for stability after bedding in. The front bipod could be screwed up and down for ranging. There was a handcrank at the end of the elevating screw housing. The Type 31 had a firing weight (mortar with bomb) of just over 20 kg (44 lb), and the M2 of 19 kg (41.8 lb). The maximum range was 1,530m (1,673yd) for the Type 31 and 1,820m (1,990yd) for the M2. Both were drop-fired weapons, in other words there was a fixed firing pin at the base of the barrel inside and when the bomb was dropped down the tube its own weight drove the ballistite cartridge on to the pin with enough force to fire the cartridge.
The Type 63 was really an updated version of the Type 31, with emphasis on portability for use in irregular and guerrilla warfare. It was much lighter in the firing position at 12.3 kg (27 lb) and had the same range as the Type 31. The basic features were the same except that there were angle plates at the rear corners of the baseplate for bedding in, rather than a rectangular spade. The Type 63 had one recoil cylinder, where the Type 31 had two. The weapon folded together for carriage, with the baseplate and bipod being placed under the barrel. Using the carrying handle on the top of the barrel, one man could easily carry it in rough country with the Number 2 mortarman carrying the ammunition. A consequence of this was that the mortar could be set up, sighted and ready to fire in a very short time. It had a slightly slower rate of fire at 15-20 rpm compared with 20-30 rpm for the Type 31 and M2, Its barrel length was also slightly shorter at 610 mm (24 in) as opposed to 675 mm (26.6 in) for the Type 31 and 726 mm (28.6 in) for the M2. All these mortars fired HE rounds, but the M2 also had an illuminating bomb, the M83.
The Soviet light mortars (M38, M39, M40 and M41) were of 50 mm calibre. The M41 50 mm did away with the bipod and shock absorber of the earlier models and used a supporting yoke which was mounted on the baseplate for elevation, traverse and cross level. Gases from the firing were ducted away from a gas regulator by a pipe under the barrel. This system was used utilised for range adjustment by rotating a sleeve in the base of the mortar which opened or closed a number of gas ports. To extend the range, the ports were all opened and to achieve the minimum range the ports were all closed. Its firing weight was 10 kg (22 lb) and it had a barrel length of nearly 600 mm (23.6 in). It fired HE rounds only and had a range of 800 m (875 yd).
MEDIUM MORTARS: 82mm mortar (CHICOM Type 20 and Type 53, Soviet M1936, M1937, M1941 and M1943)
Whilst the 82mm mortar was the standard calibre for communist forces the PRC and North Vietnam did produce 81 mm mortars mostly as copies of the American M1, with the PRC manufacturing 81mm fragmentation projectiles based on the American M43A1 ammunition. 82mm mortars (classified as 'medium' mortars) proved very popular as they combined high portability with firepower. Apart from the North Vietnamese copy of the M1, 82mm weapons in use were the Chicom Types 20 and 53 and the Soviet M36, M37, M37 New, M41 and M43.
There was little variation between these types, although the PRC (and some of the older Soviet models) fitted wheels to the ends of the bipod legs. The weapon could then be towed from the muzzle. These wheeled versions had disadvantages in stability and maintaining cross level when firing, and the Soviets abandoned the idea with the M37 New. Although the Communists' weapons were usually 82 mm, they could fire NATO 81 mm rounds. This adaptability did not apply in reverse. The Communist weapons were automatic drop fired and had quite sophisticated aiming devices attached to the barrel about half-way up its length. Some used square or rectangular baseplates (M36 and M1 North Vietnamese copy), but most had circular ones. They all used a Brandt-type bipod with elevating screws and traversing gear at the top. They all weighed around 57 kg (114 lb) and had a barrel length of about 1,200 mm (1.31yd). The rates of fire were between 15 and 25 rpm. The ranges were at a minimum about 100 m (109 yd) and at maximum approximately 3,000 m (3,281 yd). The bombs were impact detonated and weighed about 3 kg (6.61b) each. They were of HE and smoke natures. The Vietnamese developed a chemical delay fuze, which was activated on impact and delayed the explosion. This was used with HE and fragmentation rounds. The M1 copy was popular with the VC because it could be broken down into three one-man loads.
With a range of over two miles, the 82mm mortar could be considered as an ideal standoff weapon. However, weighing over 100-lbs when fully assembled, when used for standoff attacks, the crew would have to drop the rounds in rapidly and then move since counter-battery fire by US aircraft was too effective and it took time to break the mortar down into three or four carrying loads. For this reason the medium mortars were often used from established positions and the mortar either camouflaged or dismantled and hidden after use.
This was a conventional muzzle-loaded, drop-fired, smoothbore weapon. The M1937 consisted of three basic components: tube, bipod, and baseplate. The recognizable features of this mortar were the baseplate, which is circular with a flat surface across the back edge, and the bipod, which has a turnbuckle type of cross-leveling mechanism between the right leg and the elevating screw housing.
HEAVY MORTARS: 107mm (Soviet M107 and M38); 120mm (Soviet M1938 and M1943, Chicom Type 55); 160mm (Soviet M1943)
Heavy mortars, of calibres above 100 mm, were not much used by the VC as they were not as portable as medium and light mortars, but they were used by the NVA. They were all moved on a two-wheeled carriage. The USSR had weapons of 107mm (the M107/M38), two designs of 120mm (M38 and M43) and one of 160 mm (M43). The PRC Type 55 120 mm was a version of the Soviet M43. The M38 107 mm was a scaled-down version of the M38 120 mm for use by Mountain Divisions. Both could be broken down into three loads for animal pack transport, or could be moved complete on their two-wheeled carriages, towed behind any suitable vehicle. The 107mm M38 has a five-man crew, and the M107 a six-man crew. All these types could be drop fired (automatic) on to a protruding firing pin, or manually fired using a trigger device and lanyard. With the exception of the M43 160 mm they were all muzzle loaded. The 160 mm mortar was breech loaded and as a result could only be fired by lanyard and trigger. The barrel was swung upwards from the base, being pivoted on trunnions located not far from its centre point. The bomb was inserted and the breech closed. The barrel was then swung back down to the firing position. The shock from firing was absorbed by shock absorbers and a disc-shaped baseplate.
All these weapons had surprisingly short ranges when compared with NATO mortars: The M43 160mm had a maximum range of 5,150 m (5,645 yd) and a minimum of 630 m (689 yd); the M43/Type 55 120 mm had a range of 5,700 m (6,234 yd) maximum and 460 m (503 yd) minimum; M38 120 mm had the same ranges as the M43 120mm; and the M38/M107 107mm mortars had a maximum range of 6,300m (6,890yd) and a minimum of 800m (875 yd). The minimum ranges made for problems of sighting in the close country of Vietnam, and the maximum ranges left a lot to be desired - nevertheless the NVA did spectacular damage with these weapons.
107mm mortar (Soviet M107)
This mortar was a scaled down version of the 120mm M1938, reduced in weight and size to suit its normal role as the regimental mortar of mountain units in the Soviet army. Ideally suited to the NVA and VC operating in difficult terrain, the mortar could be broken down into barrel, bipod and base-plate for man-packing or else folded together for towing on a two-wheeled carriage.
120mm mortar (Soviet M1938, M1943 and CHICOM type 55)
The M1943 replaced the earlier M1938 which, when first developed, had a unique design: it consisted of four components (tube, base-plate, bipod and carriage) that could be quickly broken down for movement over short distances. For normal travel the whole weapon folded together and could be towed on its two-wheeled carriage or, if necessary man-packed in it's four component parts.
The only differences between the two weapons are that the newer M1943 had much longer shock absorber cylinders and the elevating and traversing gear was more sophisticated. Apart from these changes, the ballistic and performance details, as well as the methods of handling, remained the same.
The Chicom Type 55 was a direct copy of the Soviet M1943.
This was a conventional, muzzle-loaded, smoothbore mortar that could be either drop-fired or trigger-fired. An anti-double-loading device could be attached to the muzzle.
US Army Military Assistance Advisory Group Vietnam (MAAG) - Lessons Learned No. 71 Countermeasures Against Standoff Attacks (March 1969)
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Inside the VC and the NVA Michael Lee Lanning & Dan Cragg, Ivy Books 1994, ISBN 0-8041-0500-6
Vietnam Weapons Handbook, David Rosser-Owen, Patrick Stephens Limited, 1986, ISBN 0-85059-838-9
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