'So' was an air offensive by Imperial Japanese forces against Allied forces staging around the Guadalcanal area during the Solomon islands campaign (7/12 June 1943).

As such, 'So' was part of a Japanese effort to destroy Allied air power and shipping, and thereby slow the development of the Allied offensive to the north-west along the chain of the Solomon islands group.

'So' was a two-part offensive, each part involving a fighter sweep against Guadalcanal by several air groups of Imperial Japanese naval air service (251^st Kokutai, 204^th Kokutai and 582^nd Kokutai). Together with the following 'Se' (ii) operation, these were known collectively as the 'Lunga Air Battle'.

The first 'So' operation took place on 7 June 1943, when Lieutenant Commander Saburo Shindo of the 582^nd Kokutai led a fighter sweep based on 81 Mitsubishi A6M Reisen 'Zero' single-engined fighters (21 of the 582^nd Kokutai, 24 of the 204^th Kokutai and 36 of the 251^st Kokutai) against a variety of targets around the Guadalcanal area (including the new Allied airfield in the Russell Islands). The Japanese attackers were intercepted by a strong force of Allied fighters of various kind (Grumman F4F Wildcat and Vought F4U Corsair singlke-engined fighters of the US Navy and US Marine Corps, and Lockheed P-38 Lightning twin-engined heavy fighters and Bell P-39 Airacobra single-engine fighters of the US Army Air Force). The resulting air combats accounted for several aircraft lost on each side.

The second 'So' operation took place five days later, on 12 June, when Lieutenant Zenjiro Miyano led 77 A6M fighters (24 of the 204^th Kokutai, 32 of the 251^st Kokutai and 21 of the 582^nd Kokutai against the same targets. As had happened five days earlier, the Japanese fighters were intercepted by a strong force of Allied fighters of various kinds and the ensuing air battles had a similar result.

The Japanese lost nine and seven A6M fighters respectively in the first and second 'So' operations.