A top Senate Republican wants to know how a Russian attack submarine was able to conduct a patrol mission miles off the U.S. coastline without the knowledge of the American military or intelligence officials.

In a letter to Chief of Naval Operations Adm. Jonathan Greenert on Friday, Sen. John Cornyn (Texas) demanded “a detailed explanation of the facts” surrounding the incident in which an Akula-class nuclear attack submarine was able to sail into the Gulf of Mexico undetected.