United States Army trucks

In 1915, the US Army started testing trucks that were made to go off-road to see if they could replace horses and mules. Since then, the Army has built many different kinds of trucks or had private companies build trucks for them.
Overview.
Army trucks are measured by how many tons (907 kg) each cargo model can carry. The same type of truck can have different bodies. They also measure the number of wheels that are connected to the drive. Off-road trucks have all-wheel drive. Trucks with two axles are called 4x4, trucks with three axles are 6x6, and trucks with four axles are 8x8. Dual tires are counted as one wheel.
Until the 1990s, most Army trucks had the engine in front of the cab. In the US this is called "conventional." In Great Britain, this is called "bonneted." In the 1990s, the Army changed to new types. Most new types can have an armored cab. Medium and large trucks have the cab over the engine ("COE"). The front of the cab looks flat. Most trucks in Great Britain and Europe are COE. A new large-size truck has the cab in front of the engine ("forward control"). There are two axles under the engine. Both axles steer.
The Army uses the same parts in many trucks. They also use different parts in the same truck. A truck engine, transmission, and other parts can be from different companies. Different builders can build the same trucks.
The Army still uses many old trucks. They were built very strong and can be fitted with new engines and transmissions. The Army also uses civilian trucks. Large semi-tractors with three rear axles tow tanks on trailers. Civilian medium and heavy trucks (some with armored cabs) are also used.
The US Marines use many Army trucks but they also have their own types.
Mechanical.
Engines.
The Army used gasoline engines until the 1960s (in Great Britain, gasoline is called "petrol"). In the 1960s, they started switching to diesel engines. Some (multi-fuel vehicles) could use some gasoline or jet fuel mixed in with the diesel fuel. Now, the Army uses the same diesel engines as civilian trucks.
Almost all trucks have water-cooled inline 6 cylinder (I6) engines. Jeeps have inline 4 cylinder (I4) engines. Some -ton trucks have V8 engines. There are a few strange engines.
Transmissions.
Almost all old Army trucks had manual transmissions. Now most have automatic transmissions. A transfer case is mounted behind the transmission. It sends power to the front axle. In manual transmission trucks it has a very low gear that can go very slowly on bad ground. Automatic transmission trucks do not need a low gear.
Chassis.
A ladder frame has two rails going front to back with smaller rails connecting the two so that it looks like a ladder. A front solid driving axle is mounted on leaf springs. Tandem (two axles together) axles are mounted differently. They have leaf springs and arms to hold the axles. Some have the spring over the axles. Some have the leaf springs below the axles. A few extra-heavy-duty models use a simple but strong walking beam type.
History.
1915-1939.
In 1915, the US Army started testing trucks that were made to go off-road. They wanted to know if trucks could replace horses. Trucks could carry bigger loads and were easier to take care of. A truck can run as long as it has fuel, and a good truck should not break. A horse has to be fed and rested, and can get sick. Tests showed that trucks worked better than horses. The Army started replacing all horses and mules with trucks. One of the testers, Lieutenant Dwight D. Eisenhower, later became the President of the United States and started the Interstate Highway System.
In 1914, World War I started in Europe, and the British began buying American trucks. Trucks like the "Bulldog" Mack were good, but roads in Europe were muddy and bad.
In 1915, the United States Army was chasing Mexican revolutionary Pancho Villa in Texas and Mexico. 4x4 trucks built by the FWD Company and Jeffery Company were tested and passed. They were built for World War I. Each truck was also built by three other companies.
The Army liked to have more than one company building the same trucks because more trucks could be built. If one company had problems, the other companies could keep building the trucks. A standard "Liberty" truck was built by 15 different companies. But most trucks in World War I were made from many small companies and broke down.
In the 1920s, the Army built and tested a few trucks. The truck builders didn't do much. Then, in 1930, the Army built an test group of trucks. The standard fleet come in different sizes. They were strong and reliable, but only test trucks were built. The American truck builders said the Army was taking their business away. The Army had to stop building trucks. It was the Great Depression and the Army had very little money for trucks. Builders starting making test models in 1935. By 1939, more than 20 builders had made and improved test models.
1940-1949.
In 1940, the Army wanted all new off-road trucks. They wanted , , , and 5-ton 4x4s. They also wanted , 4, 6, and -ton 6x6s. Trucks were tested and changed. Good trucks were built in large numbers. Some good trucks were built by more than one company. (6-ton trucks were built by 5 companies.) In some sizes, more than one type were built. There were 3 different -ton trucks built. Trucks were named after their builder and model. Sometimes they were named by their size and how many powered wheels they had (-ton 6x6). "M" numbers were used to name the bodies.
During World War II, the US made a large number of trucks and loaned many to other allied countries. In 1945, all truck building ended. With the war over, there were too many trucks for the Army to use. Many were left in the countries where they had been used. Jeeps and "-ton" trucks could be found all over the world. Most were used by armies, but some were sold to civilians.
1950-1979.
After World War II, new trucks were planned. Many trucks had worked well, but there were too many types. Companies built their own types. The Army wanted types that anybody could build. They also wanted fewer types. There would be and -ton 4x4s and 2½, 5, and 10-ton 6x6s. These trucks used many of the same parts. All large trucks used the same cab. The fenders and hoods looked the same.
1950 is when the Army began using "M" numbers to namie trucks and bodies. Every truck, with every body, has its own number. (A M35 is a cargo truck and a M36 is the same truck with a longer cargo body.)
These types didn't change much for 25 years. A new Jeep (M151) was used from 1960. The -ton changed to a civilian type -ton size. The larger trucks were fixed up but were still the 1950s types.
1980-2015.
In 1980, the Army began using new types of trucks. They began to use letters to name truck types. Most of the trucks can be armored. Dual tires are no longer used on new trucks. On most trucks, the driver or other operator can increase or decrease the amount of air in the tire while the truck is moving. This is called "Central Tire Inflation System" (CTIS).
The smalles truck is the -ton HMMWV ("Hum-V" or "Hummer"). The Army started using Hummers 1983. It is made just for the Army. It is not a changed civilian truck.
The same European trucks are used for and 5-ton sizes. The -ton size has 2 axles (4x4) and the 5-ton size has 3 axles (6x6). Most parts are the same for both.
A new very heavy duty 10-ton 8x8 (4 axles) was built just for the Army. They have many bodies and some can be changed. Many have cranes to load cargo onto the truck.