Sunday, February 14, 2016

Tank Gunnery 1976, Part 7, Final Engagement HEP-T at 2000 Meters

 HEP High Explosive Plastic, muzzle velocity 2,450 fps.  

In this night-fire picture, the flat trajectory of APDS is very clear.  
HEP-T at 2,000 Meters looks very different.

Now we reached the end of Table VIII Tank Gunnery 1976.   The last engagement was a house—an 8-by-8-foot panel between 1,500 and 2,000 meters from the firing position.  The ammunition is HEP-T—High Explosive Plastic-Tracer, the slowest round that tanks fire.  The actual rounds we fired is not the service ammo pictured above but the powder-blue inert rounds. 

This final engagement was truly different from the preceding three main gun rounds because it was the longest shot with the slowest round.  When we fired APDS “SABOT” rounds at the moving tank target at 1,000 meters distance, the round is traveling just over a mile per second leaving the gun muzzle.  Even allowing for wind resistance, the time to a target roughly 3,300 feet away is less than a second.  The trajectory is essentially flat.  For a tank-sized target, it is point and shoot.

When we fired HEAT at 1,500-meter target, the muzzle-to-target time was more than a second and I could see a ballistic arc, but with a 3,850-foot-per-second speed out of the gun tube, the trajectory was still close to flat.

For the final engagement my gunner was firing at a panel nearly seven thousand feet away.  The HEP-T round has a muzzle velocity of 2,450 feet per second.  So the time to target is nearly 3 seconds (2.7 seconds with wind resistance).  When you fire SABOT at 1,000 meters, it is difficult to see the tracer at all.  Firing HEP-T at this distance, the tracer goes up, up, up in a straight line then drops rapidly at the end of its parabolic trajectory.  

As anyone knows who has watched a 70-yard touchdown pass, the ball appears to go up for 60 yards then drop rapidly in the final ten yards, right into the receiver’s hands.  Actually, the peak of the arc, whether pigskin or HEP-T round is half of the travel time form the gun muzzle to impact. 

So for this final engagement, every skill of tank gunnery was important.  When I issued the fire command, the driver had to stop on what he saw as the most solid, level ground possible.  Any tilt of the tank would send the round off target to the left or right.

For every engagement we had just fifteen seconds from the moment we identify the target until the first round goes down range.  No problem with a flat shot at 1,000 meters. 

On the other engagements, I did not have to be perfect with the range finder.  On this target, I had to have the range right or we would not hit.  While Merc, my gunner, refined his aim, I made sure I had the best possible range, that my head was straight on the head rest and the sight picture was as good as I could get. 

With every other shot, Merc had a round down range fast.  With this one he made sure his sight picture was as perfect before squeezing his electric trigger.

Then he said, “On the Way!” 

I watched the round go down range for what seemed like minutes.  The red tracer went up in a straight line then seemed to drop almost straight down toward the target. 

Before the round hit the target, the loader yelled, “Up!” then clambered up through the hatch.  He wanted to see the round hit. 

Merc had the best view in the gunner’s seat with the sight on the target. 

“Hit!” I yelled on the intercom.  “Damn,” Merc said looking through the sight. 

What I saw through the binoculars and Merc saw through the primary sight was a dust cloud rising around the target, but the most important part of what we saw was that we could see the panel for just a moment after we saw the cloud.  That meant the round strike was behind the panel.  Of course, that could mean we missed by firing over the target, but we were pretty sure the dust pattern said Hit! 

I yelled, “Fire!” 

Merc refined his sight picture then announced “On the Way!”

It looked like another hit. 

I said, “Driver Move Out.” We rolled off the range. 

As soon as the grader left the tank at the ammo point, we started yelling and clapping and congratulating each other.  We unloaded brass and rolled to the rally point.

After night gunnery, which I really don’t remember well, we scored “Distinguished.”
We hit every target during daylight gunnery and range control confirmed we put a hole in the panel on the last engagement. 

Before gunnery that year, I read the entire Dash 10 manual.  I know the TM Number as well as I know my Social Security Number.  9-2350-215-10. 

I am in Army Aviation now and have had some great flights on Blackhawk, Chinook and Lakota helicopters.  But I am not part of the crew.  For the years I was in tanks, I was crew.  It really was the best job I ever had.

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