A Thursday War is the colloquial name given in the Royal Navy for the weekly war-fighting and damage control exercises that are held during Flag Officer Sea Training (FOST), so named because they are usually held on a Thursday. FOST is responsible for ensuring that Royal Navy and Royal Fleet Auxiliary vessels are fit to join the operational fleet by testing vessels' readiness through a series of drills and exercises. These culminate in the so-called 'Thursday War', war-fighting scenarios designed to test a ship's companies' reaction to various situations and emergencies.