What became known as 'Gun Jeeps' during the Vietnam War were rather than the heavier and better protected and armed 'Gun Truck' IAV's were instead based on Jeep and other smaller vehicle bodies. This limited the amount of armour and weapons they could carry, but was compensated by their increased availability and improved speed during convoy protection operations. These up-armoured cars were used as mobile communication and monitoring hubs, as not many of the primary convoy trucks themselves had radio equipment.
The cars would drive up and down the convoys, and inform the command in the convoy about status, as well as being able to communicate using their radios with any armed 'Gun Trucks' in the convoys, which were heavily modified and similarly up-armoured and armed cargo trucks that were used for fire support and suppression during ambushes so the main part of the convoy could escape or break contact.
'Little Angel' was a Gun Jeep that has been giving armoured glass windows, metal plates on the front, side and rear while being armed with a 7.62 M60, which was the most common Gun Jeep weapon by far.
Gun Jeeps and light Dodge 37's were rarer than 2.5 or 5 Ton Gun Trucks as it was not as necessary to have as many, and they were of limited use as a gun platform, usually being armed with a 7.62 NATO calibre M60 or M1919 30. Calibre, sometimes a M2 50. Calibre or even rarer a recoiless rifle loaded primarily with anti-infantry rounds. While the M134 Minigun saw limited use on Gun Trucks it was never mounted to Gun Jeeps, due to the requirements for ammo supply and power- as it was even the lighter armed Jeeps often had the entire floor of the vehicle covered with ammunition cans for use on the guns, something that was mirrored on the Gun Trucks as well. (1)
Gun Jeeps of Vietnam
On March 22, 1968, Can Tho, RVN, we find the US 3rd Combat Aviation Battalion’s mobile security team.
Standing up in the back, manning the crank-operated 40MM MK18 grenade machine gun, is Warrant Officer Bernard Buono, creator of this heavily armed, sandbag-protected, rapid-response M151 Mutt, named the “War Wagon.”
Its mission is to rush to defend the unit’s perimeter to counter increasingly frequent and effective enemy assaults and has been up-armoured with added sandbags due to not being able to add actual armoured plates to the vehicle due the weight of the new weapons, power pack for the minigun and ammunition and remain mobile in it's role as a quick response vehicles for fending off Viet Cong attacks in the area around the FOB.
The formidable array of onboard weaponry includes the driver’s 5.56mm XM177E1 submachine gun, the passenger’s 7.62mm M134 Minigun—probably a spare from the unit’s armed helicopters—and a 40mm M79 single-shot grenade launcher resting on the back fender as Buono’s MK18 backup in the event of a jam.
The Mk18 Mod 0 was an early grenade launcher with a crank to fire the 40MM grenades with a much slower rate of fire and more likely to stutter as a result compared to later designs- they were popular with patrol boats, particularly those operating alongside the US Navy SEAL Teams but were not very reliable, hence Bernard's secondary weapon being a more normal M79 single shot 40MM grenade launcher in the event the Mk18 went down.
The Mk18 Mod 0 ''Honeywells'' were a small rushed production run (1,200 total produced) and went with the hand crank so they could get them into the field as soon as possible, using 24 or 48 round belts that were prone to falling apart due to early ones being made of fiberglass-reinforced sticky tape but later belts were better. It was always considered a stop-gap solution, had poor quality control and the goal was to replace with with a true automatic as soon as possible.
It was limited to only low velocity rounds, the same as the standard M79 single shot grenade launcher, not the later improved medium velocity 40MM such as used in the Mk19.
Range was even worse due not having a secure seal between the cartridge case and the barrel so propellant gases leaked out, which alongside the low velocity rounds with substantial arcing also affected accuracy as well, with 400M at best being considered maximum range, hence why it was mostly used by patrol boats who would be engaging riverbanks at close range with blanketed high explosive, with the major advantage of the Mk18 being the rate of fire compared to a M79.