Short answers, pulled from the story.
The Battle of Rabaul was fought on the island of New Britain in the Australian Territory of New Guinea from the 23rd of January into February 1942. A Japanese invasion force of around 5,000 troops overwhelmed the small Australian Lark Force garrison of approximately 1,400 men, capturing the port and turning it into the largest Japanese base in New Guinea.
Over 1,000 Australian soldiers were captured during the battle and its aftermath. Allied losses totaled six aircrew killed, five wounded, 28 soldiers killed in action, and more than 1,000 captured, against Japanese losses of 16 killed and 49 wounded.
The Montevideo Maru was a Japanese ship transporting at least 800 soldiers and 200 civilian prisoners of war from Rabaul to Japan. On the 1st of July 1942, it was sunk off the north coast of Luzon by a U.S. submarine, killing most of the predominantly Australian prisoners aboard in one of the greatest single losses of Australian life in the war.
Around 160 Australian prisoners of war were massacred on or about the 4th of February 1942 in four separate incidents near Tol and Waitavalo plantations. Six survivors later testified before a Court of Inquiry. Allied authorities placed responsibility on Colonel Masao Kusunose, commanding officer of the 144th Infantry Regiment, who starved himself to death in late 1946 before he could stand trial.
Rabaul provided Japan with a deep-water harbour and airfields close to the Caroline Islands, home to the Imperial Japanese Navy's major base at Truk. Controlling Rabaul allowed Japan to protect Truk and cut Allied communication lines between the United States and Australia, making it the anchor of Japanese regional defences throughout the New Guinea campaign.
Under Operation Cartwheel, Allied forces chose to isolate Rabaul using airpower rather than capturing it directly. By late November 1943, carrier-based raids had driven Japanese heavy ships from the port permanently. When Japan surrendered in August 1945, approximately 69,000 Japanese troops remained at Rabaul and it took the Allies more than two years to repatriate them.