OGDEN -- Some guessed secret Area 51 test. Others guessed alien spacecraft.
But if you were a Vietnam War veteran who said loud booms heard along the Wasatch Front on Tuesday night were "Arc Light," you were right.
Hill Air Force Base said Wednesday that B-52 Stratofortresses from Barksdale AFB, La., were conducting bombing runs at the Utah Test and Training Range on Tuesday evening.
B-52s can't go supersonic, so they don't generate a sonic boom. And they can fly so high, they can't be heard from the ground. That's one reason B-52 strikes in Vietnam, code named Arc Light, were devastating -- because the bombers flew so high they could not be heard on the ground.
The thunder of their bombs is what Utahns heard, said Hill spokesman George Jozens.
The rumbling, around 9 p.m., caused windows to rattle all over Top of Utah. Jozens said more bombing runs were expected at the range Wednesday night, weather permitting.
The University of Utah seismographic station said its seismographs didn't detect anything, but its ultra-low frequency listening devices picked up the sounds Tuesday.
Research seismologist Katherine Whidden said the listening posts normally detect noises too low for humans to hear. She said the technology is too new to quickly tell from what direction the sounds are coming.
Chris Young, a meteorologist at the National Weather Service, said with the correct conditions, loud noises from the West Desert can be heard along the Wasatch Front.
"You know, with the inverted air mass, the sound could travel along the ground, I would guess," he said. "I heard it, everybody heard it."
The B-52 is a 1950s Cold War bomber that saw extensive service during the Vietnam War.
The current Air Force Global Strike Command's B-52 is a long-range, heavy bomber that is capable of flying at high subsonic speeds at altitudes up to 50,000 feet with nuclear or precision-guided conventional ordnance with worldwide precision navigation capability.