Appearance of Shokaku from the battle of the Santa Cruz Islands (October 1942).
In September 1942, a Type 21 air-warning radar was installed on Shōkaku's island atop the central fire control director, the first such device to be fitted on any Japanese carrier. The Type 21 had a "mattress" antenna and the initial prototypes were light enough that no major structural modifications were necessary. In addition were added four triple-mount 25 mm AA guns (two on the bow and two at the stern)