The Noble (but Doomed) M551 Sheridan in Vietnam

[Ascout]

Wow. Did not know the background of the round in the late 60s. All I can say is that we didn't have a problem with the heat round and by the time I got to USAREUR the CBSS was working as intended. OTOH, some mensa decided that we would fire the HE round one gunnery at Graf. I mentioned to someone: "so let me get this straight. These were shipped to VN, sat somewhere in storage in some of the most humid weather on the planet, then shipped back when???, more storage somewhere??? and then issued to troops. What could possibly go wrong?" How about rounds breaking in half when loaded with propellant rolling around the turret floor. The things we do to satisfy project manager egos.

Well, you wouldn't have much, if any, VN-issued ammo. I was with 2/11th Cav when they finally stood down and by that time (71-72) main gun ammo was in short supply. Think about it, Vietnamization in full swing and we were trying to ship stuff the ARVN would be able to use. The M551 was not among those items (M48's were!). The Sqn. CO, who is still with us recalls main gun ammo supply becoming an issue. No M551's were left behind...not even destroyed ones. Many of the VN Sheridans were refit and reissued to Germany. These were easily identified because of the evidence of the Mine Plate kit having been uninstalled. The 14th Cav in Germany would be re-flagged in 1972 as the 11th ACR.
Once uncrated, the 152mm CC round cannot be repackaged. All our main gun ammo was sacrificed in a huge pile of ordnance we demo'ed rather than take back in from the field (and were not encouraged to return). We had a pile of ammo and explosives about 10' in diameter and man-height which was detonated after we withdrew about 500 meters.
It was spectacular.

 

[Ascout]

Wow. Did not know the background of the round in the late 60s. All I can say is that we didn't have a problem with the heat round and by the time I got to USAREUR the CBSS was working as intended. OTOH, some mensa decided that we would fire the HE round one gunnery at Graf.

What you also didn't know (and many people are loathe to hear) was the extent to which you were put at much higher than normal risk (for an armored vehicle) and you were never meant to know.
There were calculations made for the probabilities of "catastrophic failures" of the main gun. Amazingly, this did NOT include issues related to the combustible case! The target for something like this is 1:1,000,000 or better. The calculated probability for CONUS was 1:750,000. For Europe, 1:400,000. For Vietnam 1:175,000 (for reasons not due to enemy action).
When, against Combat Dev. Cmd's recommendation the M551 was declared Standard, they wrote a formal declaration that given the risks inherent in the ammo & system to crews, a letter to the Deputy Chief of Staff of the Army warning of the risk to crewman should be officially prepared, for the record. I don't believe this was done.

For my own interest, what were you told, officially, was the first round hit probability of an MGM-51 missile?

 

[Ascout]

Not to mention fog, rain, obscuration of IR tracking flares of both TOW and Shillelagh.

Countermeasures against Shillelagh were only slightly worse than what might normally occur on the battlefield, but it was an issue.
Fog and weather: Post-Vietnam I was at the Armor Board and one project was an upgraded VSS-1 Xenon searchlight. We did all the work, at night obviously, at McFarland-Oliver Special Operations Tank Gunnery Range (MFO). Ft. Knox is subject to serious fog near the Ohio River, and MFO is out Porter River Rd. and the Salt River/Creek runs down the left of the range. Just driving out and down to MFO you could go from shirtsleeves to field jacket in a few hundred meters, descending into the "bottoms". Many was the night we could not test due to fog...we'd hang out for 2-3 hours just to make it look like we were "trying", then call it a night.
In M551 Sheridan School, before Vietnam for me, we often had gunnery on the Sheridan delayed to as late as 1000 hrs. in the morning! Note the position of the sun in these pics I took at D/1/1, the M551 training company. To me, this no-go stuff for a beam rider, and we're only in Kentucky!

 

[Cedric]

Well, you wouldn't have much, if any, VN-issued ammo. I was with 2/11th Cav when they finally stood down and by that time (71-72) main gun ammo was in short supply. Think about it, Vietnamization in full swing and we were trying to ship stuff the ARVN would be able to use. The M551 was not among those items (M48's were!). The Sqn. CO, who is still with us recalls main gun ammo supply becoming an issue. No M551's were left behind...not even destroyed ones. Many of the VN Sheridans were refit and reissued to Germany. These were easily identified because of the evidence of the Mine Plate kit having been uninstalled. The 14th Cav in Germany would be re-flagged in 1972 as the 11th ACR.
Once uncrated, the 152mm CC round cannot be repackaged. All our main gun ammo was sacrificed in a huge pile of ordnance we demo'ed rather than take back in from the field (and were not encouraged to return). We had a pile of ammo and explosives about 10' in diameter and man-height which was detonated after we withdrew about 500 meters.
It was spectacular.

Apparently, we did as informed by squadron. It was the first and last time we ever fired HE.

 

[Cedric]

What you also didn't know (and many people are loathe to hear) was the extent to which you were put at much higher than normal risk (for an armored vehicle) and you were never meant to know.
There were calculations made for the probabilities of "catastrophic failures" of the main gun. Amazingly, this did NOT include issues related to the combustible case! The target for something like this is 1:1,000,000 or better. The calculated probability for CONUS was 1:750,000. For Europe, 1:400,000. For Vietnam 1:175,000 (for reasons not due to enemy action).
When, against Combat Dev. Cmd's recommendation the M551 was declared Standard, they wrote a formal declaration that given the risks inherent in the ammo & system to crews, a letter to the Deputy Chief of Staff of the Army warning of the risk to crewman should be officially prepared, for the record. I don't believe this was done.

For my own interest, what were you told, officially, was the first round hit probability of an MGM-51 missile?

Honestly, I can't remember. We generally fired one missile per year per vehicle at the TOW target at Graf which was about 2800-3000. If the missile worked, it hit. Problem was we had missiles which "poofed" out of the gun tube, went about 50m and spun around on the ground while everybody ducked.

 

[Ascout]

Honestly, I can't remember. We generally fired one missile per year per vehicle at the TOW target at Graf which was about 2800-3000. If the missile worked, it hit. Problem was we had missiles which "poofed" out of the gun tube, went about 50m and spun around on the ground while everybody ducked.

Yep, if the missile loses signal, it is "programmed" to ground itself. This is why you couldn't pull back among leafy trees or other concealment if there was any chance of the beam being interrupted by a waving leaf. Nor could you move, nor could you reload.
Time of flight to 3,000 meters was ~14 seconds, or ten times the TOF of a conventional round. And you could only sit there, motionless and in the open.

 

[rcurtner]

Yep, if the missile loses signal, it is "programmed" to ground itself. This is why you couldn't pull back among leafy trees or other concealment if there was any chance of the beam being interrupted by a waving leaf. Nor could you move, nor could you reload.
Time of flight to 3,000 meters was ~14 seconds, or ten times the TOF of a conventional round. And you could only sit there, motionless and in the open.

Don't think I would want to be a Sheridan crew member having to wait so long for a missile hit before looking for cover/concealment or being able to return fire.

 

[Ascout]

Don't think I would want to be a Sheridan crew member having to wait so long for a missile hit before looking for cover/concealment or being able to return fire.

TOF to 1500 meters was ~8-10 seconds, 2,000 meters, 10-12...3,000 meters, ~14 seconds.
You don't have to have practiced in tank-to-tank combat to realize how stupid that is. Tank round regularly traverse the battlefield in 1-2 seconds. AND, you can begin reloading as soon as the recoil is over. Not so with a missile. You had to wait until the missile either hit or missed to begin to reload (the weight of a 64lb missile being loaded would upset the gun, which as connected to the sight).
In a 1969 meeing between MICOM and the Armor community at large, it was agreed that the glacial TOF on the M551 would NOT be acceptable on the next generation MBT (then still the MBT-70). Of course, in the event, this was ignored and the same crappy system inflicted on the M60A2.

 

[Cedric]

Don't think I would want to be a Sheridan crew member having to wait so long for a missile hit before looking for cover/concealment or being able to return fire.

I had a love-hate relationship with the vehicle. I served on it for two years before I transferred to regimental HQ. It was great to go where the heavies couldn't and it was fast as heck. I mentioned before that on the automotive side of the house it was pretty reliable if the driver knew what he was doing. The LRF was great and was much better than the coincidence rangefinder on the heavies. The gun firing conventional HEAT ammo could turn a hard target into a smoldering wreck in short order. (My crew can claim a second round hit with service HEAT at 2200m) I would never count on the missile, though. We received rebuilds with all updated mods from Germersheim towards the end of their service in Europe. These were pretty good vehicles, but the handwriting was on the wall. Too much time and effort to keep them going. We turned them in and the tank sections drew new M60A1 RISE Passives and the scout sections had M113A2s and gun jeeps. The 82d light tank battalion took Sheridans to Desert Shield/Storm, but I don't know how they performed.

 

[Ascout]

I had a love-hate relationship with the vehicle. I served on it for two years before I transferred to regimental HQ. It was great to go where the heavies couldn't and it was fast as heck. I mentioned before that on the automotive side of the house it was pretty reliable if the driver knew what he was doing. The LRF was great and was much better than the coincidence rangefinder on the heavies. The gun firing conventional HEAT ammo could turn a hard target into a smoldering wreck in short order. (My crew can claim a second round hit with service HEAT at 2200m) I would never count on the missile, though. We received rebuilds with all updated mods from Germersheim towards the end of their service in Europe. These were pretty good vehicles, but the handwriting was on the wall. Too much time and effort to keep them going. We turned them in and the tank sections drew new M60A1 RISE Passives and the scout sections had M113A2s and gun jeeps. The 82d light tank battalion took Sheridans to Desert Shield/Storm, but I don't know how they performed.

Automotively it was a hoot! It stumbled in jungle environments due to cooling systems getting fouled with vegetation (the Australian field trials of the M551 found the same).
I was on the Hughes LRF test project and liked it, found it reliable. I don't think it was necessarily superior to the M17 coincidence rangefinder....it's just that the latter could not be fitted to an M551.
I believe they were mostly a "fleet in being" in DS, but for sure no tank-tank Shillelagh actions occurred. It would be the most reported tank kill since Michael Wittman!
Your experience with all the maintenance to keep them going is exactly what killed them at NTC and replaced with the OSV's. I was out there in 2003 when the fleet started being dismantled.

 

[rcurtner]

TOF to 1500 meters was ~8-10 seconds, 2,000 meters, 10-12...3,000 meters, ~14 seconds.
You don't have to have practiced in tank-to-tank combat to realize how stupid that is. Tank round regularly traverse the battlefield in 1-2 seconds. AND, you can begin reloading as soon as the recoil is over. Not so with a missile. You had to wait until the missile either hit or missed to begin to reload (the weight of a 64lb missile being loaded would upset the gun, which as connected to the sight).
In a 1969 meeing between MICOM and the Armor community at large, it was agreed that the glacial TOF on the M551 would NOT be acceptable on the next generation MBT (then still the MBT-70). Of course, in the event, this was ignored and the same crappy system inflicted on the M60A2.

Automotively it was a hoot! It stumbled in jungle environments due to cooling systems getting fouled with vegetation (the Australian field trials of the M551 found the same).
I was on the Hughes LRF test project and liked it, found it reliable. I don't think it was necessarily superior to the M17 coincidence rangefinder....it's just that the latter could not be fitted to an M551.
I believe they were mostly a "fleet in being" in DS, but for sure no tank-tank Shillelagh actions occurred. It would be the most reported tank kill since Michael Wittman!
Your experience with all the maintenance to keep them going is exactly what killed them at NTC and replaced with the OSV's. I was out there in 2003 when the fleet started being dismantled.

I had a love-hate relationship with the vehicle. I served on it for two years before I transferred to regimental HQ. It was great to go where the heavies couldn't and it was fast as heck. I mentioned before that on the automotive side of the house it was pretty reliable if the driver knew what he was doing. The LRF was great and was much better than the coincidence rangefinder on the heavies. The gun firing conventional HEAT ammo could turn a hard target into a smoldering wreck in short order. (My crew can claim a second round hit with service HEAT at 2200m) I would never count on the missile, though. We received rebuilds with all updated mods from Germersheim towards the end of their service in Europe. These were pretty good vehicles, but the handwriting was on the wall. Too much time and effort to keep them going. We turned them in and the tank sections drew new M60A1 RISE Passives and the scout sections had M113A2s and gun jeeps. The 82d light tank battalion took Sheridans to Desert Shield/Storm, but I don't know how they performed.

Have enjoyed reading yall's efforts to make the Sheridan a viable combat ready vehicle. Haven't kept up with what's going on with modern armor in today's military. Have limited info on the early Abrams. Spent a great deal of time in Germany in M-60 & A1's and M-48A3's in Vietnam, good and bad memories. Thanks.

 

[Ascout]

Have enjoyed reading yall's efforts to make the Sheridan a viable combat ready vehicle. Haven't kept up with what's going on with modern armor in today's military. Have limited info on the early Abrams. Spent a great deal of time in Germany in M-60 & A1's and M-48A3's in Vietnam, good and bad memories. Thanks.

I served on all those except the Abrams and they were solid vehicles for the time. The MGM-51/M551/M60A2 chain of debacles paved the way to the Abrams by demonstrating that you can't build a multi-million dollar tank for a few hundred thousand dollars, you have to go all in & plan to keep it in service for a LONG time. A chance the Army was finally given after the issues congress (appropriations) had gotten fed up with with little to show for it.