"Undaunted" was one of eight U-class destroyers ordered as the 7th Emergency Flotilla on 12 June 1941. The U-class were War Emergency Programme destroyers, intended for general duties, including use as anti-submarine escort, and were to be suitable for mass-production. They were based on the hull and machinery of the pre-war J-class destroyers, but with a lighter armament (effectively whatever armament was available) in order to speed production. The U-class were almost identical to the S-class ordered as the 5th Emergency Flotilla and the R-class ordered as the 6th Emergency Flotilla earlier in the year, but were not fitted for operations in Arctic waters.