M8 Armored Gun System

The United Defense M8 Armored Gun System was a light tank that was intended to replace the M551 Sheridan in the 82nd Airborne Division, as well as being expected to replace TOW-equipped HMMWVs in the 2d Stryker Cavalry Regiment (2nd ACR). The M8 project was eventually canceled. Its role in the 2nd ACR was eventually taken by the Stryker.

Development
In the 1980s, the United States Army began looking for a replacement for their M551 Sheridan tanks. Several attempts over the years to update or replace them proved unsuccessful. One of the concepts that came up was the Armored Gun System (AGS).

The M8 is the result of the AGS concept which originated in the early 1980s as a means of providing light forces with more powerful direct support. In 1980 the Army's 9th Infantry Division was selected as the test unit for the new High Technology Light Division (HTLD). The HTLD was designed to fight in the deserts of Southwest Asia. Due to several budget cuts and constraints, critical pieces of equipment needed to realize the division concept were never available. The Army was only able to field prototypes of some key pieces of the high technology equipment. In the case of the AGS, it could not even field prototypes.

A total of six prototypes were eventually built for the US Army under the designation of the XM8 AGS. The M8 was later type-classified by the US Army in late 1995 and initially slated for production in 1996.

United Defense has reportedly been seeking overseas customers, so far without success. Taiwan at one point expressed interest as a replacement for its fleet of M24 Chaffee/M41 Walker Bulldog light tanks but would not commit following cancellation by the US.

Design
The basic hull of the M8 is made of welded aluminum alloy, with a unique modular armoring system that allows the vehicle to be equipped according to requirements. The Level I (basic) armor package is designed for the rapid deployment role and can be airdropped from a C-130 Hercules and protects the vehicle against small-arms fire and shell splinters. The Level II armor package can still be carried by C-130, but must be airlanded and is designed for use by light forces in a more serious threat environment, while level III armor is designed for contingency operations and is supposed to provide protection against light handheld anti-tank weapons. Level III armor cannot be carried by C-130. All versions are air-transportable by C-5 Galaxy and C-17 Globemaster III (five and three respectively).

The M8 is armed with the M35 rifled autoloading 105 mm cannon main gun with an M240 7.62 mm machine-gun mounted co-axially. The M35 has a rate of fire of approximately 12 rounds per minute, with a ready capacity of 21 rounds with 9 more in stowage. Power is provided by a Detroit Diesel 6V-92TIA diesel developing 580 hp.

Variants
"Thunderbolt" Armored Gun System (Block II)

This technology demonstrator was a test bed to bring Future Combat System technologies to the current force in the near term. Advanced technologies incorporated into this variant include hybrid electric propulsion, band track, improved ceramic/composite armor, Second Generation FLIR Night Vision technology, digitization, a XM-291 120 mm main gun along with its 120 mm auto loader. This demonstrated system upgrade retains the M8's C-130 Hercules air transport capability, as well as the AGS 3-man crew.