From Darkest Hour: The True Story of Lark Force at Rabaul – Australia’s Worst Military Disaster of World War II, by Bruce Gamble (Zenith, 2006), Kindle Loc. 2150-2169:
The jungle, it turned out, was a great equalizer. Lieutenant Colonel Tsukamoto’s battalion encountered several impediments as they pursued the Australians, not the least of which was the heavy rain that blanketed the Gazelle Peninsula. Similarly, Lieutenant Colonel Sakigawa’s mechanized unit slowed to a crawl as they advanced around Ataliklikun Bay on January 27. “The butai could not advance as hoped,” he reported. “The mountain roads went up and down and in some places [soldiers] walked in mud and water up to the knees. And also there were obstructions on the roads [such] as fallen bamboo and rotted trees.”
Other units experienced even greater difficulty. One detachment of mountain artillery tried to drag their wheeled guns through the heavy jungle. They reached the Vudal River on January 25 only to find it impossible to ford, so the soldiers hacked out a road to a different crossing. They even labored to build a temporary bridge, but their progress was so slow that they were forced to leave the field guns in the jungle. By the time the detachment finally reached the western shores of Ataliklikun Bay, they had lost contact with the fleeing Australians.
As a result of such setbacks, the battalion commanders requested naval support. General Horii arranged for a destroyer and three transports to conduct a “sea pursuit,” resulting in the aforementioned landings at Lassul Bay and Massawa Bay, but these proved to be only a minor threat to the Australians. The Japanese did not venture inland, mainly because the jungle quickly conspired against them. As the writer of an operational report later explained: “Practically every man of the 1st Infantry Battalion suffered from malaria owing to an eruptive outbreak of the disease at the time of mopping up … in particular, the pursuit action in the Ataliklikun Bay area.”
The heavy rains and high humidity of the past several days had created ideal conditions for mosquitoes. Many of the men in Tsukamoto’s battalion, poised to capture hundreds of Australians, were themselves laid low by malaria. That so many became infected was the result of “nothing but negligence,” according to the report, which placed blame squarely on the “leaders, medical staffs and epidemic prevention staffs in particular.” Days passed before the Japanese realized what had caused the outbreak. At least ten men died, and several others were “affected in the brain and became mad.” Within days, the combat strength of the South Seas Detachment was reduced by half.