[8] The M577 is easily distinguished from the M113 upon which it is based by its raised upper hull and roof-mounted auxiliary power unit (APU).

The experience gained by the U.S. Army in the Second World War showed that close co-operation between infantry and armored forces is a necessity for combined-arms mechanized mobile warfare.

[8] Whereas tanks and armored cars offered a level of protection against weapons fire, they usually did not provide sufficient internal room to permit the extra personnel needed to operate all the radio sets.

Experience gained in the snow and mud in the Korean War showed the advantage of tracked over wheeled vehicles.

Analogue radio sets fitted to the M577 in U.S. service include:[2][8] It must be recognized that there was no such thing as a standardized M577 medical vehicle.

This role was soon provided solely by M113 "armored ambulances", and the M577 was then only used as emergency treatment vehicles (e.g. battalion aid stations).

[13] Ownership of title for and production of the M577 has changed many times over the vehicle's history due to corporate buy-outs and take-overs.

This included a yoke for steering instead of laterals (tillers), a more powerful turbocharged engine with a larger alternator increasing output from 100A to 200A, and internal spall liners for improved fragmentation protection for occupants.

In 1965 the Australian Army purchased 58 M577A1s in 1965 with some vehicles immediately shipped to Vietnam for operational duty with the 1st APC Troop.

The upgraded armor consisted of a folded aluminum plate installed under each sponson for the first three road wheels on each side of the vehicle.

In 1970, a further 38 mm of aluminum armor was fitted along the entire bottom of the hull, which greatly reduced crew and passenger casualties even from large mines.

[f] The upgrade package consisted of:[16][17] The Australian Army also operated a number of M577A1 armored ambulances, which effectively serve as both emergency treatment and evacuation vehicles.

As part of the M113 major upgrade project, 15 of these vehicles were converted to a similar AS3 standard as the ACV and redesignated as the M113AS3 armored ambulance.

At the front of the vehicle a stowage basket is attached to the engine cover in place of the trim vane, and cable cutters were mounted at each side.

[4] In German service, the M577 and M577A1 received different fire extinguishing and heating systems, modified periscopes and SEM 25/30 radios, and were known as the M577G and M577GA1 Gefechtsstandspanzer(GefStdPz) .

The K277A1 is an upgraded version with a more powerful engine and transmission, NBC protection and an automatic fire extinguishing system.

[19] Commencing service with the Republic of China Army in 1982, the CM-26 command track is a locally built variant based upon the M577A2 that shares key components from the CM-21A1 armored infantry fighting vehicle.

Unlike the CM-21A1, which varies extensively (it resembles the armored infantry fighting vehicle (AIFV)) from the M113A2 upon which it is based, changes to the CM-26 are mostly limited to its engine and transmission.

[j] The engine is coupled to a locally built automatic transmission developed by Taiwans' Industrial Technology Research Institute and is similar to the Allison TX-200-1 fitted to the M113A1/M577A1 and features four forward and one reverse gears.

[k] The vehicle is also fitted with night vision driving aids, NBC protection, improved communications suite and other minor changes.

[9][21] The M577 has been adopted by various police forces and law enforcement agencies (mostly in the U.S.[m]) as a tactical response or hostage rescue vehicle.

The driver's hatch was replaced with a transparent polycarbonate dome, and the vehicle was hermetically sealed and fitted with an overpressure air conditioning system.

On the roof of the upper hull was a "robotic miniature helicopter" (i.e. a drone) fitted with stereoscopic cameras and environmental sensors, which was remotely controlled from inside the vehicle.

In conceptual artwork the roof featured another transparent polycarbonate dome to provide external visual access to the operators, but this was not implemented on the actual vehicle.

[44][45] Only one prototype vehicle was built and is now on public display (repainted as a military ambulance) at Eagle Field in California.