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Photo # 19-N-32465-A:  Antenna of CXAM Radar on USS Chester, 6 August 1942.

Online Library of Selected Images:
WEAPONS and SENSORS -- RADAR

U.S. Navy Shipboard Radars -- CXAM

In October 1939, following the successful testing of the experimental XAF radar and several months of educating private company personnel in radar technology, the Navy contracted with the Radio Corporation of America (RCA) for six production versions of the XAF. Deliveries began in May 1940, and during the summer these were installed on a half-dozen warships: the battleship California, aircraft carrier Yorktown, and heavy cruisers Pensacola, Northampton, Chester and Chicago. With a large "bedspring" configuration antenna (17-feet by 18-feet) mounted in a rotating yoke, the CXAM was identical in configuration to the XAF and, as with the latter, the antenna could be elevated. At 5000 pounds total installation weight (1200 pounds for the antenna), this radar was suitable only for big ships. A follow-on effort to build radars with smaller antennas led, not without technical difficulties, to the SC type that was entering widespread service when the Pacific War began in December 1941.

The CXAM operated in the relatively long wavelength (1.5 meters, 200 megacycles) "P-Band", with a pulse power of 15 kilowatts. It could detect large aircraft flying seventy nautical miles away at 10,000 feet altitude, smaller combat planes at fifty miles, large ships at sixteen and destroyers at twelve nautical miles. This long-range performance against aircraft made it most useful for air search, a role it pioneered for other low-frequency, large-antenna U.S. Navy shipboard radars that served during the next many decades. Its elevating antenna was found to be of minimal value for long-range air search, but it did demonstrate potential for distant UHF communications and as an over-the-horizon radar. To save weight and similify design, the Navy's subsequent large wartime search radars, including the CXAM-1, SA, SC, SK and SR-types, had non-elevating antennas.

The CXAM's distinctive appearance makes it easy to identify in photographs taken between mid-1940 and early 1943. The cruisers Chester and Chicago originally carried their CXAM's antennas atop their mainmasts, but in 1942 these were relocated to the top of the ships' foremasts. California's radar was removed in late 1941 or early 1942, while she was under salvage in the aftermath of the Japanese attack on Pearl Harbor. This set was reportedly the one installed on the carrier Hornet in mid-1942. Northampton's CXAM was replaced by a CXAM-1 sometime before April 1942 and its further career, if any, is unknown. Those carried by Yorktown, Hornet and Chicago sank with their ships on (respectively) 7 June 1942, 27 October 1942 and 30 January 1943. Pensacola's and Chester's were damaged by shock and vibration when those cruisers were torpedoed in October and November 1942, and, if they survived to return to the United States, were replaced by more modern radars when the ships were repaired and overhauled in 1943. The CXAM on Chicago was undoubtedly the last of its type to see operational service.

Source note: Most of the information in this text is taken from the following sources: Captain L.S. Howeth, USN: History of Communications-Electronics in the United States Navy, Chapter XXXVIII (Washington, D.C., 1963); and Norman Friedman: Naval Radar (Greenwich, England, 1981).

This page features, and provides links to, a selection of images concerning the U.S. Navy CXAM type radar.

For additional information on the CXAM type radar, and on World War II era radar in general, see the Navy Department Library's "Online Reading Room" presentation:

  • " U.S.Radar - Operational Characteristics of Radar, Classified by Tactical Application" -- publication FTP 217, 1 August 1943.


    If you want higher resolution reproductions than the digital images presented here, see: "How to Obtain Photographic Reproductions."


    Click on the small photograph to prompt a larger view of the same image.

    Photo #: 19-N-32465-A

    Antenna for CXAM radar


    Mounted atop the foremast of USS Chester (CA-27). Taken at the Mare Island Navy Yard, California, 6 August 1942.
    This image is cropped from Photo # 19-N-32465. See Photo # 19-N-32465-B for for an different version of this image, darkened to emphasize the antenna wires.

    Photograph from the Bureau of Ships Collection in the U.S. National Archives.

    Online Image: 55KB; 650 x 675 pixels

     
    Photo #: 19-N-32465-B

    Antenna for CXAM radar


    Mounted atop the foremast of USS Chester (CA-27). Taken at the Mare Island Navy Yard, California, 6 August 1942.
    This image is cropped from Photo # 19-N-32465, and has been substantially darkened to emphasize the antenna wires. See Photo # 19-N-32465-A for an undarkened version, providing better details of the antenna structure.

    Photograph from the Bureau of Ships Collection in the U.S. National Archives.

    Online Image: 85KB; 650 x 675 pixels

     
    Photo #: 80-G-12147-A

    Antenna for CXAM radar


    Mounted atop the foremast of USS Pensacola (CA-24). Photographed at Sand Island, Midway, 25 June 1942. The antenna is elevated in its supporting yoke.
    This image is cropped from Photo # 80-G-12147.
    Note the forms of men working on the antenna in the center and toward the left.

    Official U.S. Navy Photograph, now in the collections of the National Archives.

    Online Image: 44KB; 650 x 675 pixels

     
    Photo #: 80-G-312018-A

    Antenna for CXAM radar


    Mounted on the foretop of USS Yorktown (CV-5). Photographed during the Battle of Midway, 4 June 1942.
    The antenna and its supporting yoke are somewhat obscured by the upper structure of the foretop, the topmast, the mast's yard (with a ladder hanging from it and signal balls on two of its halliards) and the U.S. ensign flying from the mast.
    This image is cropped from Photo # 80-G-312018.

    Official U.S. Navy Photograph, now in the collections of the National Archives.

    Online Image: 68KB; 650 x 675 pixels

     
    Photo #: NH 105858-A

    Antenna of CXAM radar


    Atop the foremast of USS Pensacola (CA-24), circa early August 1942.
    The smaller antenna of an FC (or Mark 3) fire control radar is in the lower part of the image, mounted atop the ship's main battery gun director.
    This image is cropped from Photo # NH 105858.

    Official U.S. Navy Photograph, from the collections of the Naval Historical Center.

    Online Image: 54KB; 610 x 765 pixels

     


    ADDITIONAL VIEWS: Seven ships carried CXAM radars, six (a battleship, an aircraft carrier and four heavy cruisers) receiving newly-built sets in 1940 and the last (another aircraft carrier) getting a second-hand unit in mid-1942. The views listed here for each ship show the CXAM's antenna as a small part of each image:

  • USS California (BB-44) received the CXAM in mid-1940. It was on board her during the 7 December 1941 attack on Pearl Harbor and was removed while the ship was under salvage. Subsequently employed by the U.S. Army as a shore-based air warning radar on Oahu, in the summer of 1942 it was reportedly installed on the aircraft carrier Hornet (see below).
    The following photograph shows the CXAM radar's antenna mounted on USS California:
    ===>Photo # NH 64474: USS California sinking on 7 December 1941. The antenna of her CXAM radar is visible atop her pilothouse (in the center of the image).

  • USS Yorktown (CV-5) had a CXAM atop her tripod mast at least by the beginning of October 1940. It remained on board the ship for the remainder of her career, sinking with her during the June 1942 Battle of Midway.
    The following photographs show the CXAM radar's antenna mounted on USS Yorktown:
    ===>Photo # 80-G-21931: USS Yorktown arrives at Pearl Harbor, 27 May 1942. The antenna of her CXAM radar is visible on her foretop (in the image's left center).
    ===>Photo # 80-G-13065: USS Yorktown in dry dock at Pearl Harbor, 29 May 1942. The antenna of her CXAM radar is seen edge-on atop her foretop (in the image's upper left-center).
    ===>Photo # 80-G-312018: View on board USS Yorktown during the Battle of Midway. The antenna of her CXAM radar is visible on her foretop (in the upper left of the image). For a closeup view, cropped from this image, see Photo # 80-G-312018-A.
    ===>Photo # 80-G-21666: USS Yorktown listing and abandoned, 4 June1942. The antenna of her CXAM radar is faintly visible on her foretop (in the image's center).

  • In the summer of 1942, following the Battle of Midway, USS Hornet (CV-8) had a second-hand CXAM (reportedly that removed from USS California -- see above) installed on her tripod foremast, where it replaced a smaller antenna, probably that of an SC type. The latter was remounted on the ship's after mast. The CXAM remained on board the ship for the remainder of her career, sinking with her during the October 1942 Battle of the Santa Cruz Islands.
    The following photographs show the CXAM radar's antenna mounted on USS Hornet:
    ===>Photo # 80-G-33947: Japanese airplane diving on USS Hornet, 26 October 1942. The antenna of her CXAM radar is visible on her foretop (in the image's left-center).
    ===>Photo # 80-G-34110: Preparing to abandon USS Hornet, 26 October 1942. The antenna of her CXAM radar is seen on her foretop (in the image's upper left-center). The antenna of a smaller radar, presumably an SC, is partially visible atop the after mast, in the top right-center.
    ===>Photo # 80-G-40300: Close-up view of USS Hornet's island, 26 October 1942. The antenna of her CXAM radar is partially visible atop her tripod foremast (in the top left of the image).

  • The antenna of the CXAM fitted to USS Pensacola (CA-24) is seen in a number of 1942 photographs. A post-action view shows that this antenna was missing its mounting a few weeks after the ship was torpedoed during the Battle of Tassafaronga, and Bureau of Ships "War Damage Report No. 35" (page 9) states that radar antennas were damaged by flexural vibration at that time.
    The following photographs show the CXAM radar's antenna mounted on USS Pensacola:
    ===>Photo # 80-G-12147: USS Pensacola at Midway, 25 June 1942. Her CXAM radar's antenna is seen in an elevated aspect atop her foremast (in the top left-center of the image). For a closeup view, cropped from this image, see: Photo # 80-G-12147-A.
    ===>Photo # NH 105858: USS Pensacola underway in Hawaiian waters, circa early August 1942. Her CXAM radar's antenna is seen nearly edge-on atop her foremast (in the top center of the image). For a closeup view, cropped from this image, see: Photo # NH 105858-A.
    ===>Photo # 19-N-34705: USS Pensacola anchored in a south Pacific port, 28 September 1942. The antenna of her CXAM radar is visible atop her foremast (in the center of the image).
    ===>Photo # 80-G-33862: USS Pensacola undergoing battle damage repairs, 17 December 1942. The antenna of her CXAM radar is missing from her foremast, and may have been knocked off, or damaged and subsequently removed, when the ship was torpedoed on 30 November.

  • The antenna of the CXAM fitted to USS Northampton (CA-26) is seen in several 1941 photographs. It appears to have been replaced by a CXAM-1 by April 1942.
    The following photographs show the CXAM radar's antenna mounted on USS Northampton, or show that it had been replaced by another type:
    ===>Photo #s NH 94596 and NH 95333: USS Northampton at Brisbane, Australia, 5 August 1941. Her CXAM radar's antenna is visible atop her foremast (in the top center of these images).
    ===>Photo # 80-G-32548: USS Northampton in Pearl Harbor, 8 December 1941. The antenna of her CXAM radar is visible atop her foremast (in the image's center).
    ===>Photo # NH 97808: USS Northampton refueling at sea, April 1942. The radar antenna atop her foremast is that of a CXAM-1, not a CXAM.

  • The antenna of the CXAM fitted to USS Chester (CA-27) is seen in photographs taken in late 1941 and in 1942. The 1941 photo shows it mounted on her mainmast, while those taken in August 1942 shows that it had been moved to the top of her foremast. This radar was replaced by an new SK type when the ship was repaired after her 20 October 1942 torpedoing.
    The following photographs show the CXAM radar's antenna mounted on USS Chester:
    ===>A photograph of USS Chester and USS Northampton operating in Hawaiian waters on 8-12 December 1941, shows that Chester's CXAM antenna was then mounted atop her mainmast. We do not have a reproducible copy of this photo, but believe that it one of several film frames cataloged under National Archives' Photo # 80-G-21012 (possibly 80-G-21012-S). Contact that agency concerning the availability of reproductions of this image, which shows Chester in the foreground (starboard bow surface view), with Northampton partially visible beyond her. Chester is painted in what appears to be Camouflage Measure 2.
    ===>Photo # 19-N-32461: USS Chester off the Mare Island Navy Yard, 6 August 1942. Her CXAM radar's antenna is seen atop her foremast (in the left portion of the image).
    ===>Photo # 19-N-32465: USS Chester at the Mare Island Navy Yard, 6 August 1942. Her CXAM radar's antenna is seen atop her foremast (in the top center of the image). For closeup views, cropped from this image, see: Photo #s 19-N-32465-A and 19-N-32465-B.

  • The antenna of the CXAM fitted to USS Chicago (CA-29) is seen in photographs taken during 1942 and early 1943. Those taken up through August 1942 the year show it mounted on her mainmast, while in those taken in December 1942 and later it is at the top of her foremast. This radar was lost with the ship in late January 1943, and was certainly the last CXAM in active service by that time.
    The following photographs show the CXAM radar's antenna mounted on USS Chicago:
    ===>Photo # 80-G-7293: USS Chicago and other ships at Fiji in February 1942. Her CXAM radar's antenna is atop her mainmast (in the right-center of the image).
    ===>Photo # 80-G-K-306 (color): USS Chicago and other ships off Guadalcanal, 9 August 1942. Her CXAM radar's antenna is still on her mainmast (in the right-center of the image).
    ===>Photo # 19-N-39220: USS Chicago at the Mare Island Navy Yard, 14 December 1942. Her CXAM radar's antenna is seen edge-on atop her foremast (in the top left-center of the image).
    ===>Photo # 19-N-39212: USS Chicago off the Mare Island Navy Yard, 20 December 1942. Her CXAM radar's antenna is seen atop her foremast (in the left-center of the image).
    ===>Photo # NH 55141: USS Chicago disabled by Japanese torpedoes, 30 January 1943. Her CXAM radar's antenna is seen atop her foremast (in the center of the image).


    If you want higher resolution reproductions than the digital images presented here, see: "How to Obtain Photographic Reproductions."


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    Page made 18 June 2008
    Image listing corrected and link added 30 June 2008