During the Civil War if you lived in the Allegheny River and Kiski River Valleys from Pittsburgh to Kittaning you could often here the sound of thunder yet the sky was clear.
What people where hearing was the testing of Cannons which where hauled up on flat cars on the Old Allegheny Valley Railroad
Which at one time went from Pittsburgh to Kittaning along the Right side of the Allegheny River it now stops at Arnold and is a short line industrial railroad owned by Box Car Express. at the time there where no railroads running on north side of river.
But just a mile or 2 further up the now abandoned railine where the Tarrentum Bridge is located is where they would test Cannons including the enormous for its time Rodman Cannon .
The Cannons were made at the time at Fort Pitt Foundry in Pittsburgh Strip district which was across from present day Heinz History Center
https://triblive.com/local/valley-news-dispatch/remember-when-the-sounds-of-cannon-fire-once-rang-through-the-alle-kiski-valley/?fbclid=IwAR3_vwqIIM6YMSEreTxTziEc3C7xI-KAFOqQzk5tanT7HClW6_D30Okn2uo
Which closed a decade after the Civil War.
Imagine sauteing along the Tarrentum side of the river on a sunny afternoon dressed in your best to watch across the river as the cannons where fired from the rail cars as they where too heavy to take on and off .
Had to be quite the experience. But testing of weapons has been going on in Pa. for a long time as Pa is considered the Armorer of the USA.,because all the defense contractors in Pa. and those who supply them
During WW2 Torpedoes produced in Mercer County where tested in the Pymatuning Reservoir
and at one time II- VI Corporation in Saxonburg would test the latest in infrared scope technology
at local gun ranges according to one of my gun collector friends
Since 9-11 happened most of the testing of defense contractors is kept out of public view but at one time that was a local attraction.