Later war also saw full air coverage of the Atlantic routes. I am curious when this took place. Did destroyers have radar?
From 43 onward, yes for the vast majorly of US and RN DDs. A mix before that with the RN leading the way although many USN & RN never did get it installed during the war.
Note though that most convoy escort was done by Destroyer Escorts (DE) once enough were built to free up destroyers for classic destroyer duties with the fleet. IIRC most DEs had radar. Classic fleet destroyers such as the Fletcher and Tribal classes were actually less suited to anti submarine duties due to their poor turning radius* and armament being mainly suited to anti surface and anti air. Also add in escort carriers (CVE) into the equation.
Also note I said most. Many conveys if not most had some sort of anti surface force assign to them which could also include a mix of destroyers, light and heavy cruisers and battle ships and cruisers.
*They were build for speed, DEs on the other hand only had to mainly work within relatively slow convoys. U-Boats could turn on a dime so something that could turn with them and maintain contact was needed. Speed not so much.
