The key Japanese position was on Shumushu Island, whose defense consisted of permanent emplacements protected by field and AA artillery.
All the coastal sections convenient for landings were covered with permanent emplacements and bunkers, interconnected with underground passages and trenches.
Such units were sometimes reinforced by seaplane tender Kimikawa Maru (with the 452nd Air Fleet aboard, equipped with Nakajima A6M2-N "Rufe" Hydro fighters).
There was also a Japanese air early warning radar of unspecified type on the southern cape of Paramushiro, Kurabu Zaki, but its view of Shumushu was likely blocked by the 5958-foot volcano (apparently named Suribachi, like the one on Iwo Jima) in the center of Paramushiro.
Defensive organization commanded from Rubetsu Fortress, was divided into: Etorofu District: There were probably other detached units in Habomai Archipelago (Kaigara [ru; ja] Group, Suisho, Akiyuri, Yuri, Shibotsu and Taraku island).