The T-231- an odd approach to Air Defense

The other day, friend o’ the blog Craig steered me to this post on Facebook by the Manassas National Battlefield Park:

On Saturday, May 23, a visiting family made a most unusual discovery at Manassas Battlefield. They found what appeared to be an unexploded 20th century shell while out hiking and brought it to the Visitor Center. Park law enforcement staff called in the state police bomb squad and subsequently evacuated the Visitor Center and Henry Hill. The bomb squad later confirmed the shell was inert and harmless.

First and foremost, if you find anything that even remotely resembles unexploded ordnance, do not touch it. Note the location and inform the authorities.

As it turns out, the EOD detachment was able to discern the projectile was a T-231 rocket. Which got me digging, what the heck is a T-231? Well, it was a 2.75 inch diameter (70mm) rocket projectile, sometimes referred to as HEAA.

T-231 1

t-231 2

Forgive us for not having a lot of concrete information on this, but it appears that not more than a relative handful were constructed. We infer that HEAA stands for High Explosive Anti-Aircraft. That is, in spite of the notation in the Facebook post that it was an air to air weapon, it was in  fact intended as the ammunition for a ground based anti-aircraft gun system.  What’s that, you say? How does a rocket work in an anti-aircraft gun? Well…

You may recall we’ve occasionally addressed anti-aircraft artillery and fire control here.

 

One of the challenges in anti-aircraft gun fire control is the lengthy time of flight for the shells to reach the target area. The longer the time of flight, the greater the chance the target will maneuver away from the aimpoint selected as much as an entire minute before. Remember, while a projectile fired from a cannon might have great velocity as it leaves the muzzle, it immediately begins to decelerate due to both gravity and air resistance. Thus, the closer to maximum effective range, the slower and slower the shell is moving.

If there were a way to have the velocity of the projectile remain constant over the course of its time of flight, or even just significant portion, that would simplify the fire control problem.  A rocket, of course, accelerates as long as its motor continues to burn, until it reaches its maximum possible aerodynamic speed.  Rockets of those days were, however, somewhat inaccurate weapons.

And so it appears the Army tried an intriguing approach to combining both a gun and a rocket into one weapon. The T-231 was packed inside a recoilless rifle shell casing. That is, it had an open end and was fired from a recoilless rifle. The firing charge imparted a relatively modest muzzle velocity of about 1000 feet per second to the round. The initial charge also served to ignite the round’s rocket motor, which then boosted it to a velocity of about 3000 feet per second, roughly on par with the muzzle velocity of existing anti-aircraft guns. But the small size of the projectile meant there was a correspondingly small rocket motor (and less size for a warhead as well) and that limited the burn time for the motor.

in flight

Launcher

T-231 3

The program never really went beyond a handful of test firings, mostly to gather data. The performance wasn’t significantly better than existing anti-aircraft artillery, and the first generation of guided missiles was just reaching operational status at the time, rendering the project obsolete.

Craig did point out one mystery yet to be solved. The test firings apparently took place at Wallops Island. So how did the projectile find its way to Manassas? We may never know. 

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