SUDBURY -- An underground military complex in North Bay built to withstand a four-megaton nuclear explosion is going to be decommissioned.

Operating from 1963 to 2006, the underground complex at 22 Wing North Bay was a key NORAD (North American Aerospace Defense Command) facility during the Cold War, when western democracies were at odds with the former Soviet Union.

The complex was designed to withstand a nuclear bomb 267 times more powerful than the one the U.S. dropped on Hiroshima during the Second World War -- and continue operating.

In 2006, the complex was partially decommissioned and its operations moved to a modern, aboveground facility located at the 22 Wing base.

After review, the underground complex was declared surplus to military needs in July 2012.

"While several parties have expressed interest in repurposing the facility, due to its location underneath an active military base and NORAD facility, transferring the facility to a third party is not possible," Capt. Leah Pierce, public affairs officer, said in an email.

"As a first step, we need to examine our options by completing various studies which will help us determine costs and timelines for proposed and recommended options. That starts today as we release an advanced procurement to complete these studies."