Geoffrey
Do you have a source for that?
The reason I ask is that Parshall & Tully devoted Appendix 8 in "Shattered Sword" to the question of whether the Japanese had radar at Midway and followed up on the reports from a couple of Japanese officers interrogated at the end of the war that Hiryu had radar during Operation C in the IO. Those contradicted statements from other officers. Then John Prados in "Combined Fleet Decoded" made reference to Hiryu's post Op C action report that said she had some new form of detection gear that had a blind spot at the rear.
As you note, the source is John Prados, he provides the citation that presumably Parshall and Tully followed up on and discovered went missing sometime between 1995 and 2005. Parshall and Tully have done a good job and are most probably right. The following is the small holes in what they present. Mainly as Japanese can be a very difficult language to translate. Both Prados and Parshall and Tully provide excepts, not the full section of the report.
The Short Survey of Japanese Radars notes Detectors was the name for early warning sets. The quote talks about search installations which Parshall and Tully define as exclusively non electronic. Next is "many times when the first warning was the splash of bombs", I am trying to remember when the carrier force was actually bombed before April 1942.
"install AA search radar or sound equipment" radar is not a Japanese term in 1942, not British then either, as far as the RAAF was concerned its units were called radio stations until end 1942, then RDF, then Radar from 1 September 1943.
Parshall and Tully state it was many weeks of dockyard work to install one of the then Japanese naval radars and state Kaga had far too small superstructure for a set, yet looking at the diagrams Hiryu's superstructure is larger, but is it really so much that Kaga is "far too small"? They are assuming the entire system was in the superstructure and takes weeks to install. Looking at Shokaku, which did get a search radar, its superstructure was not enlarged to do so.
It leaves an unlikely possibility Hiryu had an experimental installation in the Indian Ocean, removed or not working at Midway, given the quality issues the Japanese electronics industry had. In any case detecting the incoming is one thing, the IJN did not have the controlled intercept system, relying on the ships to signal or use their guns to show where the enemy aircraft were.
On another note
Australian War Memorial - AJRP