 Chalker initially served with SEAL Team One and was later hand-selected by Commander Richard Marcinko in 1980 to become a plankowner of the Navy's first dedicated counter-terrorist unit, SEAL Team Six.As a member of SEAL Team Six, he participated in Operation Urgent Fury in the US Invasion of Grenada.His team reached then Governor General Paul Scoon's mansion and held it for an entire day while being attacked by a force of Grenadians and Cubans.