Discovered some U.S. Submarines were being upgraded with AN/APR-1
Info listed about it at this site:
http://hereford.ampr.org/millist/m3.html
AN/APR-4 is dated 1943 info listed here:
http://www.radiomilitari.com/apr4.html
http://www.navsource.org/archives/08/08390.htm
[quote]By late 1944, many submarines had limited radar detection installations called radar countermeasures (RCM), although they never included jammers.
Plaice's (SS-390) antenna blocked out here appears to be an AS-44, which detected microwave (S-band) signals at 1000-3500 MHz seerving an APR-5AX or SPR-2. Both antennas were omnidirectional, and both could be connected to a pulse analyzer (SPA-1), from which the signal's pulse repetition rate and pulse width could be read. If the radar was a known type, this figure could identify it.
http://www.navsource.org/archives/08/0839024.jpg