[greasepaint]

was MacArthur involved,
or was it all Navy / M.C.?

my understanding is that the
Army got involved at some point

[GATOR NAVY]

The Army, yes. They were not part of the initial invasion but Army forces joined the Marines as the battle continued. MacArthur, no. MacArthur commanded the South West Pacific Area with his HQ in Australia. Guadalcanal was part of the South Pacific Area commanded initially by Ghormley with his HQ in New Caledonia. Ghromley was relieved by Halsey.

[GATOR NAVY]

Or I should say Ghromley was relieved by Nimitz, technically for medical reasons but really because Nimitz lost confidence in his abilities to fight. Halsey was Ghromley's replacement.