Peter West From Bolt action Australia already gave us the scoop on this but listed now with an image and blurb, due October 2019:
Bolt Action: Campaign: Mariana & Palau Islands
The Mariana and Palau Islands campaign, also known as Operation Forager, was intended to facilitate the recapture of the Philippines and to provide bases for the bombing of the Japanese mainland. This new Campaign Book for Bolt Action allows players to refight the fierce battles of Saipan, Peleliu, Guam, and many others. With new, linked scenarios, rules, troop types, and Theater Selectors provide plenty of options for both novice and veteran players alike.