That sound of an explosion you might have heard late afternoon on Monday, July 14, was the detonation of two 20 millimeter machine gun rounds that had been found in Joe English Pond in New Boston.

The rounds were uncovered in the process of clearing old scrap metal from the bottom of the pond and its shore. The area was a target for T51 Mustangs and Avenger aircraft, which used it as a bombing range during World War II through 1956.

The planes would fly over the site, taking off from Grenier Field, which later became the Manchester Airport.

The detonation on July 14 occurred during a technical demonstration at the base on how to detect and remove unexploded ordnances. The Air Force relied on remote controlled robotic devices to do the work, according to Lt. Col. Dean Bellamy, the operations officer at the base.

Air Force officials find the metal with ground penetrating radar. A robotic excavator with a 4,400-pound magnet attached to it extracts the metal from the ground, Bellamy said. The excavator is controlled by an operator in a van more than 1,800 feet, or six football fields, away. Once the live rounds were uncovered, an explosive disposal team was called to the area to detonate it.

He said the bullets were placed with a C-4 explosive in a hole that had been dug and covered with a type of protective plastic tarmac. No one was injured and no property was damaged in the detonation, according to an Air Force press release.

The Air Force said public awareness of the clearing process is key. If a resident comes across what they think might be bombs, bullets or other ordnance, they should contact the base at 471-2417.

“Safety is priority No. 1, and we thank the local citizens for helping us maintaining the safety of this installation and the surrounding communities,” said Lt. Col. Kevin Reigstad, commander of New Boston Air Force Station. “The safe disposal of these machine gun rounds is an example of how careful demolition processes will result in safe and thorough range clearance work here.”

Prior to the detonation, the base said it had notified abutters through an e-mail list managed by the town of New Boston. Clearing of scrap metal will continue through the summer.

The Air Force said it will be covering approximately 1,400 acres on the base starting next month. The project will take about 120 days.