She was assigned to the Port Moresby Operation (Operation MO) tasked with the occupation of the Australian Territory of New Guinea in order to isolate Australia and New Zealand from the United States. The operation was also to seize the islands of Tulagi and Samarai, and the Deboyne Islands (where seaplane bases were to be established) as well as Nauru and Banaba Island (due to their valuable phosphate deposits). "Tama Maru" was assigned to the Tulagi invasion force commanded by Rear Admiral Kiyohide Shima and consisting of the flagship minelayer/cruiser , 1 auxiliary minelayer ("Kōei Maru"), 2 destroyers ( and ), 5 minesweepers ("Tama Maru" along with , , "Hagoromo Maru", and "Noshiro Maru No. 2"), 2 subchasers ("Toshi Maru No. 3", "Tama Maru No. 8"), and 1 transport () carrying 400 men of the 3rd Kure Special Naval Landing Force. The light carrier provided air support accompanied by 4 cruisers (, , , ) and 1 destroyer (). The force departed from Rabaul on 30 April 1942 and on 3 May 1942, landed on Tulagi unopposed. "Shōhō" with its escorts left the area to support the main Port Moresby operation which allowed planes from of Task Force 17 under Rear Admiral Frank Jack Fletcher to attack the ships of the invasion force. On 4 May 1942, "Tama Maru" was patrolling with "Wa-1" and "Wa-2" north of Savo Island when it was spotted by a squadron of Douglas TBD Devastators from the Yorktown. "Wa-1" and "Wa-2" were immediately sunk while "Tama Maru" was significantly damaged and sank on 6 May 1942.