Pilot online readers reported that the planes were loud enough to shake houses in Palo Alto County, and could be heard from Milford into Sac County. A sonic boom apparently produced by one of the planes was reportedly heard as far away as Lytton.
"It sounded like someone ran into the house or something landed on the roof," one local person described the experience.
According to media reports, numerous booms have recently been reported in several U.S. states and elsewhere in the world. The booms result from planes exceeding the speed of sound, about 750 mph at sea level. In some cases, military officials have confirmed the noises and shocks being reported have been caused by test flights of F-22 Raptor jets combined with certain atmospheric conditions that cause the booms to carry for greater distances than normal.
Some have suggested the rash of booms may reflect changes in military testing policy, a step-up in domestic preparedness efforts, or testing of new equipment - speculation that the military is not commenting on.
Recent military policy has called for faster-than-sound testing to be done over water as much as possible to avoid alarming the public. Supersonic operations over land are supposed to be conducted above 30,000 feet or if lower, in designated, lowly-populated areas.
Twenty-one Air National Guard F-16 fighters capable of breaking the sound barrier are based in Des Moines, although the media there has reported on a potential Air Force budget cut that could remove them in fiscal 2013, or replace them with remotely-piloted aircraft.
A Sioux Falls fighter wing also employs F-16s, and reported in 2012 that it is doing night flying for a week at a time about once a month, in exercises that include intercepting small suspect aircrafts.
Flight exercises were a common sight over the region years ago, when Sioux City hosted a fighter wing that employed the F-100 starting in 1962, then the A-7D Corsair II starting in 1977, and the F-16 Fighting Falcon from 1991-2003, when it was converted to a refueling wing, with eight massive KC-135R Stratotankers.