Ro-33 was laid down on 8 August 1933 at the Kure Naval Arsenal in Japan, launched on 10 October 1934, and commissioned in November 1935. She was the lead submarine of her class - the K5 sub-class of the Kaichu type, a refinement of the preceding KT boats with greater surface speed. Two diesel engines of 1,450 horsepower each drove her on the surface at 19 knots, with a range of 8,000 nautical miles at an economical 12 knots. Submerged, 600-horsepower electric motors pushed her to 8.25 knots in short bursts, or stretched the battery to 90 miles at 3.5 knots. She was not enormous. She was not cutting-edge. She was exactly what the Imperial Japanese Navy expected of a medium submarine in the 1930s, and for a while she did her job.

Ro-33 served in the South China Sea, the Indian Ocean, and the southwestern Pacific. She operated in support of the Japanese invasion of British Malaya in December 1941, the invasion of Java in early 1942, the Battle of the Coral Sea in May 1942, and the opening moves of the Guadalcanal campaign. When U.S. Marines landed on Guadalcanal on 7 August 1942, the 8th Fleet ordered Ro-33 - along with Ro-34 and other submarines - to proceed to Indispensable Strait off Guadalcanal, scout the Allied anchorage at Lungga Roads, and make contact with Japanese forces ashore. She did all three. She also delivered food to Japanese troops at Cape Esperance on 13 August and scouted Savo Island on 15 August, reporting that the Allies had set up an observation post on the island's northwest coast. She returned to Rabaul on 16 August, safely, her captain and crew presumably tired.

Six days later, on 22 August 1942, Ro-33 sailed from Rabaul on what turned out to be her final patrol. Her assignment: a patrol area off Port Moresby, supporting the Japanese push across the Owen Stanley Range in the New Guinea campaign. By 25 August she was off southeastern New Guinea, south of Samarai. On 26 August she transmitted a routine status report announcing her arrival in her patrol area. After that, nothing. The Japanese never heard from her again. The radio silence that followed was normal enough for a submarine at war - submarines ran silent by profession - but silence lasted longer than it should have. Eventually her loss became obvious. Only the circumstances took time to sort out.

On 29 August, the 3,310-ton merchant ship Malaita left Port Moresby bound for Cairns, Australia, escorted by HMAS Arunta. The escort was there because Japanese aircraft had been raiding the Gulf of Papua. Nobody was expecting a submarine. At sometime before 12:45, west of Port Moresby in the Gulf of Papua, a torpedo from Ro-33 struck Malaita on her starboard side, under the bridge. She listed so hard to starboard her crew abandoned ship at 12:45, certain she was about to capsize. She did not. Her crew eventually returned, and she was towed back to Port Moresby. The torpedo had done its damage - but not enough to sink her. Meanwhile, Arunta was hunting the shooter.

Arunta's sonar found Ro-33 ten nautical miles southeast of Port Moresby. Four depth-charge attacks, starting at 13:05, produced the oil slick that told the Australian crew what they'd done. Depth-charge warfare was brutal and impersonal - a destroyer dropping canisters set to explode at a depth, while below, unseen men felt the hull flex, heard the plates crack, and listened as the pressure equalized from whatever leak opened first. On 1 September 1942, the Imperial Japanese Navy declared Ro-33 presumed lost off Port Moresby with her entire crew of 70. The navy struck her from its list on 5 October. Seventy Japanese sailors - sons, husbands, fathers - who never came home from a patrol off a New Guinea port most of them had probably never heard of before it was their turn to die there.