Just to let you know, the game "cheats", beginning January 01, 1938, and continues all the way through December 31, 1945...
- so they basically have it from the get-go in the game
However, in real life, quoting from the Introduction to the E-07 Report of the US Naval Technical Mission to Japan 1946:
ELECTRONICS TARGETS
JAPANESE RADAR COUNTERMEASURES AND VISUAL SIGNAL DISPLAY EQUIPMENT
The Japanese had reached approximately the stage in countermeasures development that was reached in the United States in 1942. The Army took the lead in electronic jamming, although the Navy appears to have made the most effective use of "window", which was employed quite extensively by both services.
The Army and navy had several types of intercept receivers of mediocre design, and accompanying antenna which provided a fair method of direction finding. There was nothing of intelligence value in test equiment, visual display or analyzing equipment.
Anti-jamming was understood only dimly, and there was no basic research on anti-jam circuits of techniques. The Japanese claimed some success in reading through "window" and "rope", but were helpless in the face of electronic jamming.
basically speaking, they did not have much, but radar itself could pick-up signals, so if they paid attention to their radar screens... which wasn't ever widespread, like the US had it on PT boats, but they did have a good portion of some classes with it...
Now, as to what "windows" and "rope" are, I do not know... code for something top-secret back then...
