The conning tower of the STo Type boat 1-402. The boat’s Type 22 surface search radar (the funnel-like device) is evident; behind is the air warning radar. Also visible are binoculars for the bridge watch crew. On the aft part of the conning tower is a 25mm single mount.

Radar One of the Imperial Navy’s foremost shortcomings during the Pacific War was its failure to develop radar. This had a crippling effect operationally on its submarine force. The lack of an air warning radar on Japanese submarines increased their vulnerability to air attack, especially at night. This was crucial given the already excessive diving times of Japanese submarines. The Type 13 was the standard Japanese air search radar for submarines; however, it was not until April 1944 that this bulky radar was adapted to submarine use. Performance was mediocre, with the capability to detect a group of aircraft at 60 miles (97km) and a single aircraft at 30 miles (48km). To detect Allied radar, Japanese submarines also employed passive measures. The E27/Type 3 radar detector was introduced well before the Japanese fitted radar to submarines; however, its reliability was suspect. Additionally, late-war Japanese submarines had their hulls and conning towers covered by an antiradar hull coating designated “LI.” The standard surface search radar was the Type 22. This set had two horn-shaped antennae, one for transmission and one for receiving. On most submarines, the Type 22 was mounted in front of the conning tower. Performance against a large surface target was reportedly in excess of 21 miles (34km), but was probably much less on a submarine where the set was mounted fairly low to the water.

It is likely that other subs had Type 22 radar installed late in the war. The dates of installation for most of these ships are as of commissioning. Only I-54 and I-56 would have had it installed later in the subs named below.

While the Japanese had a good program underway when the war ended, their lack of early effort meant that they were always behind the Allies in their advances. Japanese radar of 1945 was roughly equivalent to that employed by the US in 1942 and 1943, while at that point the Americans and British had advanced fire control radars in common service with both anti-ship and anti-air capability. By the end of the war the Americans were also expert in the use of radar to vector combat air patrol onto incoming attackers, making their fighters far more effective.