Skip to comments.The FReeper Foxhole's TreadHead Tuesday - M551 Sheridan Light Tank - Jul. 20th, 2004
Posted on 07/20/2004 12:02:28 AM PDT by SAMWolf
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Airborne Assault Vehicle
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.
The M551 Sheridan, from just off the assembly line at the Cleveland Tank Plant
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.
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.
In early 1972, laser rangefinders AN/VVG-1 were 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.
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).
This view shows the M551's unusual driver's hatch in the open position. The hatch rotated around the driver, removing the need for an adjustable-height seat for open-hatch operation, and also eliminating the worry of turret rotation over the driver's exposed head. The black container on the hatch to the mannequin's right is the periscope washer fluid reservoir. The smoke grenade launchers on this vehicle are mounted in a line, however the original design featured a metal bar mount that ran under the grenade launcher assemblies.
(Picture taken 1 Dec 1990 by Spc. Henry; available from the Defense Visual Information Center.)
The gun-launcher on this M551A1(TTS) lacks a bore evacuator, so this vehicle is equipped with the closed-breech scavenging system. The guidance unit for the Shillelagh missiles is mounted above the base of the gun-launcher. The commander's weapon station has been fitted with armor protection, and additional machine gun ammunition could be stowed around the circumferance of the turret. The laser rangefinder transceiver is visible just above the spare ammunition box, and the cable cover runs around the right side of the cupola. The smoke grenade launchers are mounted over the brackets for the older style grenade launchers, which had four tubes on each side of the turret mounted linearly instead of clustered. One-hundred fifty-two millimeter ammunition is stored with protective bags around the combustible cartridge case; the bag is removed before firing.
The surf board is in the fording position and the swim screens, stored in chambers running along the upper edges of the hull, are fitted together. It wasn't pretty but it met the Army requirements.
The M551 Sheridan tank was designed in the early 1960's, as a need arose for U.S. forces needing a light tank. Constructed of aluminum armor, it is extremely fast, using a 300 hp Detroit Diesel engine and cross drive transmission. It mounts a steel turret and an aluminum hull. It was air transportable and fully amphibious with the screen around the sides raised. The main gun fired a 152mm standard projectile or a missile. It packed a lot of punch for a small tank. A similar gun was also used on the M728 Combat Engineer Vehicle. It is equipped with nuclear, biological, and chemical protection for the crew of four men. This enables it to fight in almost any climate or situation. The vehicle has seen combat use in Vietnam, Panama and Desert Storm, and it is used today for training in the California desert by the Armored Force Opposing Forces training center. Weight is 34,900 lbs. Top speed is 43 mph. It was built by the Allison Division of General Motors.
The M551 Sheridan was developed to provide the US Army with a light armored reconnaissance vehicle with heavy firepower. The main armament consists of an 152mm M81 gun/missile launcher capable of firing conventional ammunition and the MGM-51 Shillelagh antitank missile (20 conventional rounds and 8 missiles). Due to problems with the gun-tube-launched antitank missile, the Sheridan was not fielded widely throughout the Army. The gun would foul with caseless ammuniton, gun firing would interfere with missle electronics, and the entire vehicle recoiled with unusual vigor when the gun was fired, since the 152mm gun was too big for the light-weight chassis. The Shillelagh missles were evidently never used in anger. In addition to the main gun/missile launcher, the M551 is armed with a 7.62mm M240 machine gun and a 12.7mm M2 HB antiaircraft machine gun. A Detroit Diesel 6V-53T 300hp turbo-charged V-6 diesel engine and an Allison TG-250-2A poweshift transmission provide the Sheridan's power. Protection for the four-man crew is provided by an aluminum hull and steel turret. Although light enough to be airdrop-capable, the alumninum armour was thin enough to be pierced by heavy machine-gun rounds, and the vehicle was particularly vulnerable to mines.
Initially produced in 1966, the M551 was fielded in 1968. 1,562 M551s were built between 1966 and 1970. The Sheridan saw limited action in Vietnam, where many deficiencies were revealed. The missle system was useless against an enemy that employed tanks, though the Sheridan saw a lot of use towards the end of the war because of its mobility. Sheridan-equiped units participated in Operation Just Cause in Panama (1989), and was deployed to Saudi Arabia during Operation Desert Shield. As projectile technology advanced, the Sheridan's potential declined and it was phased out of the US inventory beginning in 1978. The M551 was last used by the 82nd Airborne Division. Some 330 "visually-modified" Sheridans represent threat tanks and armored vehicles at the National Training Center in Fort Irwin, California.
The engine for the M551 was a General Motors 6V53T, V-6 cylinder, supercharged, 2-stroke diesel engine. It produced around 300hp at 2800rpm and could push the AFV at over 43mph on level roads. The 158gal of diesel could fuel the Sheridan for 350 miles between fill ups. The white transmission is seen to the right in this photo and is at the rear of the engine. This left side view shows the radiator and cooling fan to the left in the picture, the cylinder head cover along the top and exhaust manifold covered with foil insulation along the side. The canister mounted upright on this side, near the top/rear of the engine, is the coolant surge tank and the other cylinder seen horizontal behind it is the supercharger. Down below is the cylindrical oil filter and the engine breather drain connection is at the very bottom of the block.
National Training Center M551 Sheridans
Initially, the power plant had problems with over-heating and its huge plume of black diesel smoke ("rooster tail") was a burden for the vehicle's primary role of recon. A later Product Improvement Program (PIP) decreased the smoke signature by adding a throttle delay feature and exhaust deflector. The original aluminum alloy engine block that was prone to heat warping was also replaced with a cast iron block that eliminated that problem.
An interesting idea that could have been made to work and work well it seems.
But what could have been done I have no idea..
Cool! Do you have any you'd like to share with us?
Guess not. I'm awake now. :-)
Cool morning here in the Pacific NW.
Good morning alfa6.
What did I miss? Why were they removed?
Psalm 27. A good prayer to use in the fight against the left that hopes to destroy us.
Good morning Mayor.
Oh my. Might be a day to hit the mall or a movie to stay cool. Morning Gail.
What a great poster! Thanks PE.
Hello feather. Post us one of those Doolittle pics?
My guess is that there were no armored targets to engage.
From my desk.
LOL. That DUH would be from me. Sorry, forgot to make sure you were signed off my computer before I posted.
I found it at the US Navy histroical site. ;-O
I know, I do too. But, we are to remember to hate the sin amd not the sinner.
It's not an easy task when you see what some people do and stand for.
The whole democrat party platform is against Gods laws..
Look at my reply to Sam..
I agree BTW..
I had to post it....
1 The LORD is my light and my salvation; whom shall I fear? the LORD is the strength of my life; of whom shall I be afraid?
2 When the wicked, even mine enemies and my foes, came upon me to eat up my flesh, they stumbled and fell.
3 Though an host should encamp against me, my heart shall not fear: though war should rise against me, in this will I be confident.
4 One thing have I desired of the LORD, that will I seek after; that I may dwell in the house of the LORD all the days of my life, to behold the beauty of the LORD, and to enquire in his temple.
5 For in the time of trouble he shall hide me in his pavilion: in the secret of his tabernacle shall he hide me; he shall set me up upon a rock.
6 And now shall mine head be lifted up above mine enemies round about me: therefore will I offer in his tabernacle sacrifices of joy; I will sing, yea, I will sing praises unto the LORD.
7 Hear, O LORD, when I cry with my voice: have mercy also upon me, and answer me.
8 When thou saidst, Seek ye my face; my heart said unto thee, Thy face, LORD, will I seek.
9 Hide not thy face far from me; put not thy servant away in anger: thou hast been my help; leave me not, neither forsake me, O God of my salvation.
10 When my father and my mother forsake me, then the LORD will take me up.
11 Teach me thy way, O LORD, and lead me in a plain path, because of mine enemies.
12 Deliver me not over unto the will of mine enemies: for false witnesses are risen up against me, and such as breathe out cruelty.
13 I had fainted, unless I had believed to see the goodness of the LORD in the land of the living.
14 Wait on the LORD: be of good courage, and he shall strengthen thine heart: wait, I say, on the LORD.
The entire LAW with container takes up less space than the ammunition for the RPG. You don't have to reload the LAW, you just grab another one.
You can reload a recoiless rifle such as the 90mm faster than you can an RPG and it is not much heavier. The laucher for the RPG 7 is not that light.
You didn't have anything to shoot the missles at plus one could have been captured and the design compromised. We had the same system in the M60 A3 that we had in Germany to defend against the communist hordes.
Alas, snippy, I would love to do that, but no longer have control of the photos. I gave them to my Uncle Fran's sister in 1997.
Nice poster. Gen. Doolittle didn't look a thing like Alec Baldwin!
Nice job on the thread. Thanks for being upfront about the "warts" on the 551. Thankfully, I never was assigned to a Sheridan unit. One look at that main gun ammo was enough for me.
Afternoon Darksheare. Just proves that not all ideas can be translated into a usable, functioing product.
Sometimes for me it's an impossible task.
OOOOOOO! Nice one!
I have no idea on the weight of an RPG launcher, IIRC the LAW wasn't too bad. The idea of ruunning around with 3 or more RPG rounds strapped to my back isn't real appealing either.
The Sheridan could have been so much different.
Pretty much guaranteed that if it were redesigned today, it'd look similar to the two man/three man light scout tank that congress canceled recently.
Thanks. I got some close up looks at the Sheridan, I tend to like the MBT's and the Sheridan just doesn't qualify. :-)
Plus you have to carry the launcher.
Howdy back atcha PE. I like your tagline today.
Thanks for the explanation.
So what's your favorite tank?
Well, my favorite tank is the Abrams. The USA really hit a home run with the M-1, not that I'm partial to home cooking don't you know.
My favorite historical tank is a toughie, sometimes I'm partial to the Tiger and sometimes the Panther.
You gat that right it took us a long time but we finally developed and fielded the best tank in the world. The one thing that amazed me though was the lack of the ability to fire an HE round. I wonder who came up with that idea originally.
It's great to be back to understanding only 10% of "Treadhead Tuesday"!
Hey, call me ignorant (okay . . . ignorant!) but I can't believe this tank was created in the 60s and is now retired?!?!?
You mean that donkey spawn that was supposed to leave the coutry 4 years ago?
Mr. Gates brainchild leaves alot to be desired.
Hi w over w. Sam says it was a POS as a tank. I guess looks ain't everything. ;-)
She's a beauty.
I LIKE IT! It's my opinion the long after people forget bill clinton they'll still remember Neil Armstrong.
We REALLY REALLY need to go back. It's what we do, see what's over the next hill.
Amen. I know because of him we all have pc's basically but geez e pete he could have closed a few holes along the way!
Fortunatly God isn't limited the way we are.
Something to remember, we're still in the model T age when it comes to computers.
Now what I want is a system that does what I want it to do, not what I tell it to do.