"Critical equipment identified by investigation officials has been recovered, including the Voice and Data Recorder, often called the black box," US Air Force Special Operations Command spokeswoman Rebecca Heyse said.

"The equipment will be transported to laboratories for data retrieval with follow analysis of the data at AFSOC. We expect the analysis process to take several weeks," Heyse said by email.

Seven bodies had previously been recovered and Heyse said the search for the eighth crewmember was ongoing.

The aircraft crashed in waters off southern Japan on November 29.

The Osprey, which can operate like a helicopter or a fixed-wing turboprop plane, has suffered a string of fatal accidents in recent years.