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M551
M551A1(TTS)

152mm Gun-launcher Armored Reconnaissance/Airborne Assault Vehicle M551 Sheridan^1-13

As can be surmised from the designation, the M551 Sheridan was intended to fill a multitude of roles. It was a light airdroppable tank, a reconnaissance vehicle, and was able to take on enemy armor thanks to its 152mm combination gun/missile launcher. The driver's hatch was unusual in that it rotated around the driver on a vertical axis, while the commander's cupola hatch and loader's hatch were more conventional. M551's hull was ringed by a lightweight structure filled with closed cell polystyrene foam for buoyancy, and a flotation screen could be raised to allow the vehicle to float across water obstacles. There were four smoke grenade launchers on either side of the turret which were supported by a brace on early vehicles. Early M551s had a turret ventilator dome on the left rear side wall; this was moved to the turret left front on later Sheridans. Three types of 6V53T engines were used during production: the 6V53T Model 5063-5395 was an older design with a cast-iron engine block; Model 5063-5398 used an aluminum engine block; and Model 5063-539F was a newer design of cast iron engine block.

The original M81 152mm gun-launcher on the M551 was equipped with a bore evacuator and an open breech carbon dioxide scavenging system, which was composed of two jets that blew CO₂ into the open breech after firing to get rid of any remnants of the combustible case ammunition. However, this system also blew any burning pieces of left over combustible cases around the turret, which was unpleasant for the crew and deadly with the rest of the ammunition around. A closed breech scavenging system (CBSS) was developed by Allison to remedy this problem. CBSS blew any remaining pieces of the ammunition out of the weapon while the breech was still closed. CBSS was first installed on M551 number 700, and retrofit kits were developed for the previous vehicles. In vehicles with CBSS, ammunition stowage was reduced to a total of 29 rounds and missiles since one of the air cylinders replaced an ammunition rack.

The 152mm gun-launchers differ in the following ways: M81 was fitted with a bore evacuator and the open breech scavenging system; M81 Modified was an M81 retrofitted with the CBSS; M81E1 had a shallower missile keyway to reduce firing stresses on the barrel, and the barrel was thickened near the muzzle. When CBSS was introduced, the bore evacuator was omitted from new-production gun-launchers. With the CBSS operating, upon firing a round the turret ventilating fan turns off and the gun-launcher recoils and returns to battery. The CBSS then activates, making a foghorn-like sound for two seconds, after which the breech opens and the ventilating fan returns to operation.

The MGM-51 Shillelagh missile was a SACLOS infrared-guided missile fitted with a shaped-charge warhead. MGM-51B extended the maximum range to 3km from the MGM-51A's 2km, and the MGM-51C was fitted with a shorter key compatible with the M81E1 gun-launcher. Sheridans 140 through 223 and 740 through 885 were produced without the missile guidance hardware. The 8x telescope M119 was replaced during production with the 8x or 12x telescope M127.

In early 1972, the laser rangefinder AN/VVG-1 was fitted to the commander's cupola, and the transceiver replaced the forward vision block. The rest of the laser rangefinder was mounted behind the commander, and a cable cover ran around the right side of the cupola from the transceiver to the rear of the TC's position. Sheridans fitted with the laser rangefinder were designated M551A1. M551A1s also replaced the gunner's M127 sighting telescope with the M127A1, which provided protection against laser light, and the cupola could be aligned with the main gun-launcher automatically.

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152mm Gun-launcher Armored Reconnaissance/Airborne Assault Vehicle M551A1 (Tank Thermal Sight) Sheridan^1-5

In early 1989, the tank thermal sight from the 105mm gun tank M60A3(TTS) was also fitted to the M551A1. These vehicles were known as M551A1(TTS).

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References

1. Hunnicutt, R.P. Sheridan: A History of the American Light Tank, volume 2. Navato, CA: Presidio Press, 1995. Reprinted with permission from Sheridan, R.P. Hunnicutt ©1995, available from Presidio Press, 505B San Martin Drive, Suite 160, Navato, CA 94945.
2. TM 9-2350-230-10 C2 Operator's Manual: Armored Reconnaissance/Airborne Assault Vehicle, Full-tracked, 152-mm Gun-launcher, M551A1 (NSN 2350-00-140-5151) and M551 NTC (2350-01-115-1579). Washington, DC: Department of the Army, 5 September 1995.
3. TM 9-2350-230-12 C14 Operator and Organizational Maintenance Manual: Armored Reconnaissance/Airborne Assault Vehicle, Full-tracked, 152-mm, M551 (2350-00-873-5408) and M551A1 (2350-00-140-5151). Washington, DC: Dept. of the Army, 3 May 1976.
4. TM 9-2350-230-20-1 Unit Maintenance Manual for Hull, Suspension, and Miscellaneous Hull Components of the Armored Reconnaissance/Airborne Assault Vehicle, Full-tracked, 152-mm Gun-launcher, M551A1 (NSN 2350-00-140-5151) and M551 NTC (2350-01-115-1579). Washington, DC: Department of the Army, 1 June 1996.
5. Federation of American Scientists. "M551A1 Armored Reconnaissance Airborne Assault Vehicle (Sheridan)." DOD 101. 12 September 1998. 25 April 2001 <http://www.fas.org/man/dod-101/sys/land/m551a1.htm>. DOD 101
6. TM 9-2350-230-10 Operator's Manual (Crew) for Armored Reconnaissance/Airborne Assault Vehicle, Full-tracked, 152 mm Gun-launcher M551 (2350-00-873-5408) and M551A1 (2350-00-140-5151). Washington, DC: Headquarters, Department of the Army, 10 June 1976.
7. TM 9-2350-230-25P/2 C7 Organizational, DS, GS, and Depot Maintenance Repair Parts and Special Tools Lists Turret, Elevating and Traversing Systems, Cupola, Gun-launcher, and Fire Control and Missile Guidance Control Materiel Used on: Armored Reconnaissance/Airborne Assault Vehicle: Full-tracked, 152-mm, M551. Washington, DC: Department of the Army, 19 April 1974.
8. TM 9-2350-230-35/2 C13 Direct Support, General Support, and Depot Maintenance Manual Turret, Elevating and Traversing Systems, Cupola, Gun-launcher and Mount for Armored Reconnaissance/Airborne Assault Vehicle: Full-tracked, 152-mm, M551 (2350-00-873-5408), M551A1 (2350-00-140-5151), and Opposing Forces (OPFOR) (2350-01-115-1579). Washington, DC: Headquarters, Department of the Army, 22 January 1986.
9. Crismon, Fred W. U.S. Military Tracked Vehicles. Osceola, WI: Motorbooks International, 1992.
10. Miller, David. The Illustrated Directory of Tanks of the World. Osceola, WI: MBI Publishing Co., 2000.
11. Holloway, Mark. "M551." E-mail to the author. 2 December 2001.
12. Holloway, Mark. "RE M551." E-mail to the author. 2 December 2001.
13. TM 9-2815-205-34 C2 Direct Support and General Support Maintenance Manual Engine, Diesel: With Container (NSN 2815-00-124-5390) Composed of: Engine, Diesel: (Detroit Diesel-GMC Model 5063-5299, Series 6V53) and Container Assembly (NSN 8145-00-138-7809) and Engine Diesel: With Container (NSN 2815-00-909-5949) Composed of: Engine, Diesel: (Detroit Diesel-GMC Model 5063-5398, Series 6V53T) and Container Assembly (NSN 8115-00-999-5356) and Engine Diesel: With Container (NSN 2815-01-031-6154) Composed of: Engine, Diesel: (Detroit Diesel-GMC Model 5063-5395, Series 6V53T) and Container Assembly (NSN 8145-00-999-5356). Washington, DC: Headquarters, Department of the Army, 31 March 1975.

Last updated 9 Sep 2024.
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