TITTABAWASSEE TWP, MI -- A yellow submarine sits on a trailer in Freeland, preparing to take explorers on a voyage. It's not the 10th album from The Beatles, but an actual yellow submersible.

Greg Busch, owner of Busch Marine Inc., said the sub will be used by University of Michigan researchers to explore the Alpena-Amberley Ridge beneath Lake Huron.

The PC1201 is 23 feet long, 8 feet wide and can accommodate two passengers and a pilot.

Busch said the sub has been all over the world, including Antarctica.

The next voyage, however, will take it to a prehistoric time.

Researchers believe there is a 9,000-year-old caribou hunting structure in the Alpena-Amberley Ridge.

The area used to be dry land at one time but now is covered with 120 feet of water, Busch said.

"Nobody's never looked at that area," Busch said. "They think there may be some significant prehistoric things in that area."

Sub service

Busch offers international underwater services that include manned charters, observation remote-control vehicles, work class remote-control vehicles, hydrographic surveys, side scan sonar surveys, vessel charters and marine construction.

The sub can be used for film production, tourism, salvage and casualty investigations and underwater inspections of pipelines, cables, dams, bridge footings, wrecks and structures.

"Whenever there is a big oil spill, a lot of the oil goes to the bottom of the water," Busch said. "We have been contacted to go down and survey it."

Originally built in 1976, Busch said the sub has to be taken apart and rebuilt every three years.

"The last major overhaul was one year ago," he said.

Hunting for artifacts

According to an anthropology report prepared in 2014 by researchers from U-M, Wayne State University and the Nautilus Marine Group International, the Alpena-Amberley Ridge was a dry land corridor that connected northeast Michigan to southern Ontario 9,000 years ago.

"The site and its associated artifacts provide unprecedented insight into the social and seasonal organization of prehistoric caribou hunting," the report states.

"When combined with environmental and simulation studies, it is suggested that distinctly different seasonal strategies were used by early hunters on the (Alpena-Amberley Ridge), with autumn hunting being carried out by small groups, and spring hunts being conducted by larger groups of cooperating hunters."

Researchers are expected to begin voyages to the site in July or August, according to Busch.