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 .