The Truck, Utility, 1/4-Ton, 4×4, M151 or simply M151 was the successor to the Korean War M38 and M38A1 jeep Light Utility Vehicles. Commonly referred to as "jeeps" or "quarter-tons", the M151 had an integrated body design which offered a little more space than prior jeeps, and featured all-around independent suspension with coil springs. It has since been replaced by the larger AM General HMMWV in most utility roles in frontline use. With some M151A2 units still in U.S. military service in 1999, the M151 series achieved a longer run of service than that of the WW2 MB/GPW, M38, and M38A1 series combined.
In 1951 Ford Motor Company was awarded the contract to design a 1/4 ton 4×4 truck to replace the aging M38 and M38A1 model jeeps. The M151 was developed to specifications and guidance of the U.S. Army's Ordnance Tank Automotive Command. Design started in 1951 and testing and prototyping lasted through most of the fifties. Although the M151 was developed and initially produced by Ford, production contracts for the M151A2 were later also awarded to Kaiser and AM General Corp, a subsidiary of AMC.
Although the M151 mostly retained the same basic layout and dimensions of its predecessors, it was for all intents and purposes a completely new design. Unlike previous jeep designs, whose structure consisted of a steel tub bolted onto a separate steel frame, the M151 utilized a integrated frame design, which integrated the box frame rails and the sheet-steel body into a unibody structure. Eliminating the separate frame gave the M151 slightly more ground clearance, while at the same time lowering the center of gravity. Although the vehicle's dimensions were only slightly enlarged — the 85 inch wheelbase was 4 inches longer than its predecessor, or 5 inches compared to the Willys MB, and the width was increased 3 inches — combined with the improved space efficiency of the integrated body design, the vehicle was a bit roomier than previous jeeps, while retaining the same light weight.
Another area improved upon in the M151 was the suspension. Dispensing with the rigid live axles in the front and rear that all previous military jeeps used (a layout still used on modern day Jeeps, such as the Jeep CJ and Wrangler), the M151 was instead equipped with independent suspension and coil springs. This made it capable of high-speed, cross-country travel, while boasting high maneuverability and agility. The new suspension also had the added benefit of providing a more comfortable ride.
Due to copyright and trademark issues, the M151 did not feature Jeep's distinctive seven vertical slot grille, instead, a horizontal grille was used.
Unlike other military transports, such as the WWII and Korean War Jeeps and Dodge and Chevrolet transport trucks, the M151 was never widely released into the civilian market. This was partly because it did not meet federal highway safety standards for civilian vehicles, and because of a series of rollover accidents. While the high pivot rear swing axle geometry on the M151A1 was responsible for the rollovers, injuries and fatalities, the industry (Ford and the Army) claimed that they were primarily due to driver errors, with operators unprepared for the increased performance compared to the Jeeps, which it replaced. The swing axle rear suspension design was prone to significant camber changes when subjected to cornering, resulting in the rear lifting, the outside wheel tucking under which often led to a vehicle rollover. Steering input as commonly found in a high-speed emergency avoidance maneuvers or hard cornering, was a recipe for disaster. The vehicle's tendency to lose control was reduced when there was weight in the rear, so drivers would often place an ammunition box filled with sand under the rear seat when no other load was being carried. The box could simply be emptied or abandoned when the extra weight was not needed. Recoilless rifle carrier models were especially prone to rollover accidents due to their stiffer rear springs and were typically subjected to severe speed restrictions any time the gun was not aboard.
Ford Motor Company designed the M151A1 beginning in 1951. By 1965 the world knew of the problems with swing axles (e.g. “Unsafe at Any Speed” by Ralph Nader). Nevertheless when, in 1969, an automotive engineer at the Human Engineering Lab at Aberdeen Proving Ground wrote a report that included: 1) an analysis that showed the high pivot swing axle in the M151A1 was inherently unstable under cornering, 2) retrofits that had proven to solve the problem on Corvairs, VWs, and Formula Vees and, 3) ways of designing a replacement. The Director of the Human Engineering Lab rejected this report and when the solutions were forwarded to the Ford engineers they rejected them as well.
The handling issues were eventually resolved by a redesign of the rear suspension, introduced in the M151A2 model. However, due to liability concerns, the U.S. Department of Defense deemed all M151 series vehicles "unsafe for public highway use", limiting their public use. Continuing problems with vehicle roll-overs into the 1980s led the US military to retrofit many M151 series vehicles with the "Roll over protection structure" (ROPS), a roll cage intended to protect both front and rear seat passengers.
First put into service in Vietnam, the M151 played an active part in American military operations well into the 1980s, when it was phased out in favor of the HMMWV. Despite its official replacement, the M151 had some distinct advantages over its much larger and heavier successor, like being small enough to fit inside a CH-53 heavy transport helicopter. This flexibility was one of the reasons the U.S. Marine Corps deployed M151 Fast Attack Vehicle (FAV) variants up until 1999, in theatres such as Kosovo. It currently serves in U.S. special forces units as a FAV.
Various models of the M-151 have seen successful military service in 15 different NATO countries and M151s were sold to many countries, including Canada, Denmark, the United Kingdom and non-NATO countries like Egypt, Lebanon, Israel, the Philippines, and Pakistan. Currently, the M151 is used by over 100 countries worldwide.
In the late 1980s the M151s began being phased out of service in favour of the HMMWV. A few (perhaps 1,000) were sold via Government Surplus auctions, and those that were not sold via Foreign Military Sales (FMS) overseas were cut into four pieces and scrapped. However some individuals were able to buy these "quartered" M151s and simply weld the four sections back together, and rebuilt them into drivable condition. Some vehicles sold in the United States were simply cut in half, some of which were simply welded back together and driven. Additionally, beginning in the late 1990s a few companies dealing in Military surplus items bought M151s from some of the foreign governments that received the vehicles via FMS for reconditioning and further sales.
Growler Manufacturing and Engineering designs and sells the Internally Transportable Light Strike Vehicle based on the M151 drivetrain. The Internally Transportable Light Strike Vehicle is intended to replace Fast Attack Vehicle variants of the M151, and is reduced in size to fit into the V-22 Osprey tiltrotor transport. Although originally intended to utilize the M151 drivetrain, the final result is an all new design and contains no M151 parts or design elements.
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