To meet its requirements for an armoured personnel carrier, El Salvador built a mild-steel prototype based on the chassis of the old US unarmoured M37B1 (4 × 4) ¾ ton truck. Trials with this prototype showed that it lacked ballistic protection. The government of El Salvador then turned to the US for assistance and the US Army Tank Automotive Command's RDE Center's Design and Manufacturing Technology Directorate became involved.

After studying the first prototype in El Salvador in February 1985 it was apparent that the country lacked the facilities to build the required numbers of vehicles.

Tank Automotive Command then offered a three-part plan to El Salvador. First, to build the prototype of the APC in its own facilities in Detroit and then take it to El Salvador to be used as a reference model. Second, to pre-cut dual-hardness armour and carry out critical welding on the side panels, side rails and windshield before shipment to El Salvador, with a total of 66 kits to be provided. Finally, to train a team of El Salvadoreans in the US in welding techniques.

This package was accepted by El Salvador and after carrying out some redesign work, including changing the driver's compartment doors and rear crew compartment doors from a flush to a surface mount design, modifying the rear fenders and cutting the hood configuration straight across in front of the windscreen, the first prototype was completed in Detroit in March 1985.

Trials in the US showed that the armour could not be penetrated by 5.56 mm ball ammunition fired from a range of 25 m. This was followed by two days of mobility trials during which the prototype was driven over 500 km of varying terrain.

In April 1985, the prototype was shipped from Tank Automotive Command for its flight to El Salvador, 74 days after receiving the go-ahead. In May 1986, TACOM shipped the last of 66 kits to El Salvador, which assembled them at the rate of two a week.

By late 2007 it is estimated that about 41 of these vehicles remained in service, with 15 of these being weapons carriers and 26 in armoured personnel models. Description

The Cashuat is essentially an M37B1 (4 × 4) truck chassis fitted with an armoured body to protect the occupants from small arms fire. Dual-hardness armour protects the crew compartment, high-hardness armour protecting less crucial areas. Kevlar is fitted inside the troop compartment and on the outside of the 12.7 mm turret. At present, belly armour is not fitted.

The layout is conventional with the armour-plated engine compartment at the front, driver and vehicle commander to its immediate rear, and the troop compartment at the very rear of the hull. Both commander and driver have a forward-opening side door with a bulletproof window in the upper part and a firing port underneath. To their front is a bulletproof window with a firing port underneath and armour protection is provided above their position. Provision has been made for installing a radio.

The open-topped troop compartment is at the rear and the troops normally enter and leave via two outward-opening doors in the rear that have a firing port on either side. An additional three firing ports are provided in the upper part of each side of the troop compartment. There are no associated vision devices with this firing port.

Before being fitted with the new armoured body, the chassis was stripped down, cleaned and reinforced, the suspension was uprated, and new brakes, shock-absorbers and springs were fitted.

The tyres are filled with a Du Pont component to allow the vehicle to travel up to 90 km with a perforated tyre. Variants

There are two versions of this vehicle in service with the El Salvadorean Army. One is the armoured personnel carrier, which has a crew of two and carries eight fully equipped troops. The second version is a gun carrier and is fitted with a manually operated armoured one-person turret, to the immediate rear of the commander and gunner, which is armed with a .50 (12.7 mm) M2 HB machine gun and a 7.62 mm M60 machine gun and shield, mounted either side towards the rear.

Some vehicles have also been fitted with wire mesh screens to neutralise RPG-7-type rocket propelled unguided anti-tank projectiles before they contact the main armour of the vehicle.

More recently, some of these vehicles have been upgraded further by replacing the existing front and rear axles with new axles taken from 2.5 t (US) (6 × 6) Reo trucks. Two .50 (12.7 mm) M2 machine guns have been installed on the roof of the vehicle.