I read a memoir of Saburo Sakai an Imperian Japanese Naval Pilot during World War II. One of the things that surprised me was how he described the Zero fighter as not being equipped with a Radio. Communication between pilots was done using hand signals.
How was it seen as acceptable by the Japanese to omit radios from their Aircraft? How were they able to perform so well in the early years of the war without such a key piece of equipment?
The A6M Zero had a radio as standard issue on the plane. You likely are reading this in reference to the occasional case where the radio of the plane was taken off in order to give the plane extended range. This was typically done in cases where planes were to redeploy to various locations in the Pacific. In addition, in some cases pilots exercised radio silence to not give away their position, instead using hand signals to coordinate.
The most famous example of Japanese radio use in their aircraft was the "Tora Tora Tora" message that signified the success of surprise at Pearl Harbor. So they most certainly had radios on their planes by December of 1941.