Former Navy sailor Robert Patrick Hoffmann II was sentenced this week to 30 years in prison. Hoffmann, 40, was convicted last fall of attempted espionage.

According to the U.S. Department of Justice, Hoffmann had attempted to pass on top secret information to agents he believed to be working for Russia. In fact, those agents were part of an FBI investigation into the retired sailor and his willingness to sell U.S. secrets.

Hoffmann served 20 years in the U.S. Navy before retiring in November 2011. While in the Navy Hoffmann was worked as a cryptologic technician for submarines, operating electronic systems for those submarines. As part of his position Hoffmann held multiple security clearances and was trusted with privileged U.S. national defense information.

In 2012, the FBI began investigating Hoffmann. FBI agents posing as Russians contacted Hoffmann and established an understanding that he would be willing to sell defense information. Eventually Hoffmann suggested only physical meetings and a dead drop site was established at the base of a tree in Virginia Beach. Hoffmann made three different drops at the site, delivering thumb drives filled with the answers to the questions posed by the fake Russian agents, including secret and top secret national defense information.

“By attempting to hand over some of America’s most closely held military secrets, Robert Hoffman put U.S. service members and this country at risk,” said John Carlin acting assistant attorney general. “ Today, Mr. Hoffman is being held accountable for his actions. This prosecution should serve as a warning to others who would compromise our nation’s secrets.