In the 1950's, to equip the American 82nd and 101st Airborne Divisions with some type of air-droppable heavy anti-tank weapon, the unsatisfactory M56 Scorpion was introduced. The vehicle provided insufficent protection for the crew (most were only protected by the 90mm gun shield) and the cannon was too powerful for the chassis, frequently pushing it back several feet when fired. In the early 1960's, a replacement was sought. At the same time, the US Army was also looking for a new armored reconnaissance vehicle, the M41 Walker Bulldog being over a decade old. The M551 Sheridan was the result, entering production in 1966 and service in 1968, but proved little better than the vehicles it replaced and in some ways markedly worse.
While the steel turret was moderately well-armored and sloped, the aluminum hull was vulnerable to heavy machineguns and mines (in Vietnam, hitting a mine with an M48 medium tank generally left the tank immobile but easily repairable and the crew alive, while with the M551 the driver was usually killed and major repairs were needed). On the bright side, there were reports than rocket-propelled grenades had some difficulty penetrating the polystyrene foam-filled hull sides (to aid floatation) -- this may be treated as an unreliable form of laminate armor, at the GM's option. Early Sheridan's had no armor shield for the commander when standing in his hatch or operating the A/A MG. However, after experience in Vietnam where several commanders were killed, a front and rear shield for the hatch was often mounted (PD/DR 4/25). The vehicle was partially amphibious, requiring a small floatation screen to be raised.
However, of all the M551's problems, it's main armament was perhaps the biggest. The 152mm M81 was designed to fire both conventional ammo (HEAT-T-MP, white phosphorous, TP-T and -- used to very good effect in Vietnam -- cannister) and the MGM-51 Shillelagh command IR-guided missile, which had started development in 1959. The two related amament problems were: (1) when the missile was fired, the rocket residue tended to foul the barrel and (2) when conventional ammo was fired, the recoil (which was really too much for such a light vehicle) often knocked out the gunner's missile guidance hardware. In any event, no MGM-51's were ever fired in combat.
Some 1700 Sheridans were built from 1966 to 1970, with most now out of service. The US Army got rid of the M551's in the recon role in 1978 while the 82nd Airborne kept theirs until 1996 (with no replacement in sight). Aside from Vietnam (where some 60-65 saw action), M551's also saw service in Operation Just Cause (Panama, 1989) and were among the first vehicles on the ground in Operation Desert Shield with the 82nd Airborne division. Some 330 were visually modified and used at the NTC at Fort Irwin as enemy vehicles, most serving as T-62s.
Other models:
M551A1: The first 700 hundred Sheridans had problems with hot debris
from the breech being drawn back into the turrent when the cannon breech
was opened. A new system was devised (and was also retrofitted to existing
tanks) which blew the debris out the barrel. The air tanks for pressurization
reduced missile load to eight. The M240 also replaced the M73 as the coaxial
MG. Also, a laser rangefinder was added for the commander and anti-laser
vision blocks were provided for the driver.
Note: Data on the M551's armor thickness is difficult to find. I used values from the game Steel Panthers III from SSI, Inc. as they seemed a reasonable guess. Some sources listed 1,562 being built; I chose the higher figure.
Subassemblies: Body +3, full rotation Turret +3, ten Open Mounts
-1 (#1 partial rotation, #2-10 fixed), two Tracks +2
P&P: 221 kW turbocharged diesel w/tracked drivetrain, 2x
4320 kWs lead-acid batteries (provision for two more for cold weather operations),
132 gallons diesel (fire chance: 8) in self-sealing tank, 370 mile range
(road)
Occ: Body: 1 CS (driver); Turret: 2 CS (commander, gunner, loader)
Cargo: 10 cf internal
| Armor | F | R/L | B | T | U |
| Body | 6/110 | 4/55 | 4/55 | 4/25 | 4/25 |
| Turret | 6/270 | 6/135 | 5/135 | 4/25 | 0/0 |
| Tracks | 4/20 |
Equipment
OM1: .50-cal M2 MG in universal mount
OM2-9: one smoke discharger each (four total on left/right of
turret)
OM10: white/IR searchlight (1 mile)
Turret: gunner day gun sight (8x telescope, +3/+5), gunner active
IR night gun sight (3 miles, Scan 16), 2 medium range radios
Body: driver passive IR sight (1 mile, Scan 10), 4-man NBC kit,
compact fire suppression system
Statistics
| Size: 10'x9'x21' | Payload: approx. 5,000 lbs | Lwt: 34,800 lbs (17 tons) |
| Volume: 1210 cf (Size Mod: +5) | Maint.: 40 hours | Price: $300,000 |
| gSpeed: 43 | gAccel: 3 | gDecel: 20 | gMR: 0.5 | gSR: 4 | GP: very low (4/5) |
| wSpeed: 4 | wAccel: 0.3 | wDecel: 10 | wMR: 0.5 | wSR: 5 |
New Weapons
152mm M81 gun/launcher: short barrel, low-powered, smoothbore,
breechloading
Dam 6dx10 (5) [10d] HEDP, malf Crit, Acc 12, SS 25, 1/2Dam 750, Max
4100, ROF 1/8
MGM-51 Shillelagh anti-tank missile: HEAT warhead, communicator
guided (laser)
Dam 6dx15 (10), SS 20, Min 100, Max 5700, Speed 320 yps, End 18 sec,
ROF 1/20, AWt 59 lbs
Notes:
A. Malfunction depends on a couple of factors, described in the color
text. In general, use the following two rules:
(1) If a missile is fired, there is a 4-in-6 chance of the barrel fouling
- drop Malf to 16 the first time, with a -1 each additional fouling, until
the barrel is cleaned.
(2) If a conventional round is fired, use the rule on p.VE104, except
that the guidance system is knocked out on a 15+.
B. Infared guidance, as the MGM-51 uses it, does not exist in VE 2/e.
Use the rules for laser communicator guidance.
Sources
The Illustrated Encyclopedia of Military Vehicles, Ian Hogg
and John Weeks, 1980
Modern Fighting Vehicles, Bob Lewis, 1988
http://www.fas.org