I haven't been able to find the date of introduction of the U.S. YE/ZB homing system. Does anyone know where to look?
Here, this overview notes that the system was first installed aboard USS Saratoga (CV3) in May 1938.
http://www.skywaves.ar88.net/Docs/YE-ZB Presentation.pdf. Also see this which repeats the wording on the 1938 Saratoga installation
https://www.nrl.navy.mil/system/files/content/75awards.pdf
The RN had a similar system first tested in 1934 and first installed on a carrier in 1936, see:
https://www.nonstopsystems.com/radio/pdf-hell/article-part3a-1947-Quinn.pdf
Robert Cressman's
USS Ranger 1934-1946 notes on page 157 with regard to a yard period in 1941: "The Ranger shifted to the Norfolk Navy Yard on the morning of 12 July, and her air group assumed shore-based status. Soon, the usual tumult of a yard overhaul would be familiar to the ears of the ship's company, as the ship began to undergo repairs and alterations which included installation of 1.1-inch quadruple-mount antiaircraft machine guns to replace the 3-inch/.50-caliber guns, a CXAM-1 radar and YE homing gear."
Can't pin down when Yorktown (CV5) had her system installed. My father, who went aboard, a F4F-3 driver, with VF-42 in June 1941, to remain aboard until the bitter end in June 1942, said that they did not have it installed then but did have it when they left for the Pacific in mid-December 1941. Yorktown received the CXAM installation in May 1940 at Pearl Harbor and an IFF modification at Norfolk in the days immediately before heading west.
Can't pin down Enterprise either, but the VB-5 action report for the raid on the Marshalls of 1 February 1942 notes: "The YE-ZB equipment proved invaluable. Without this aid planes may have been lost and it is certain much valuable time would have been wasted."
I'd suggest that after mid to late 1941 the YE/ZB installations were complete aboard existing carriers and standard installation on new ones coming off the ways.