WASHINGTON (AP) — Senate investigators are blaming China for nearly two dozen successful hacker break-ins of computer networks belonging to Pentagon contractors.

A yearlong investigation announced Wednesday by the Senate Armed Services Committee identified at least 50 intrusions since 2012 against unspecified contractors working for the U.S. Transportation Command, or Transcom. It said at least 20 break-ins were highly sophisticated and blamed those on China’s government.

Investigators said China’s military was able to steal emails, documents, user accounts and computer codes. They said it compromised systems aboard a commercial ship contracted by Transcom for logistics routes, and hacked into an airline the U.S. military used.

The newly declassified Senate report says defense contractors have generally failed to report to the Pentagon hacker break-ins of their systems as required under their business agreements.