[Crosseye76]

Here is one from the Wiki on CXAM radar:

"
The CXAM radar system was the first production radar system deployed on US Navy ships. It followed several earlier prototype systems, such as the NRL radar installed in April, 1937 on the USS Leary (DD-158); its successor, the XAF, installed in December, 1938 on the USS New York (BB-34); and the first RCA-designed system, the CXZ, installed in December, 1938 or January, 1939 on the USS Texas (BB-35). Based on testing in January, 1939, where the XAF was more reliable, the US Navy ordered RCA to build six XAF-based units for deployment and then shortly thereafter ordered 14 more.
The first six units RCA produced (delivered in 1940) were denoted "CXAM" and were a fusion of XAF and CXZ technologies. These were installed on the USS California (BB-34), the USS Yorktown (CV-5) (in September, 1940), and four cruisers. The next 14 units RCA produced (also delivered in 1940) were denoted "CXAM-1" and were slight improvements over the CXAM design. These were installed on the the USS Texas (BB-35) (in October, 1941), USS Pennsylvania (BB-38), USS West Virginia (BB-48), USS North Carolina (BB-55), and USS Washington (BB-56); on the aircraft carriers USS Lexington (CV-2), USS Saratoga (CV-3), USS Ranger CV-4), USS Enterprise (CV-6), and USS Wasp (CV-7); on one heavy cruiser; on two light cruisers; and on the seaplane tender USS Curtiss (AV-4).
Radar detection range of aircraft depends on altitude, size, and number of aircraft. The CXAM is listed (in U.S. Radar, Operational Characteristics of Radar Classified by Tactical Application) as being able to detect single aircraft at 50 miles and to detect large ships at 14 miles. Other sources list CXAM detection range on aircraft out to 100 miles.
The US Army's first non-prototype radar system, the SCR 270 radar, was developed in parallel with the CXAM."


Even though the Wiki calls them 'production' sets, I think they were still pretty much prototype sets or low-rate production test sets to try them out in the field, and the designation seems to reflect that. When the first real production line sets were made in large quantities, they were given the standard designations.