"Ro-34" began her third war patrol on 27 February 1942, putting to sea from Cam Ranh Bay bound for a patrol area in the Indian Ocean south of Java and southeast of the Lombok Strait and Tjilatjap, Java, to support the upcoming Japanese invasion of Java. In early March 1942, she was on the surface off Noesa Kembang lighthouse on Kambangan Island south of Tjilatjap when she sighted a patrolling Allied corvette. When she submerged to avoid the corvette, she became entangled in a net — either an antisubmarine net or a fishing net — at a depth of . During several attempts to break free, she depleted her batteries, and after sunset her commanding officer ordered her to surface and engage the corvette with her deck gun. She broke free of the net in the process of surfacing, and came to the surface in the midst of group of fishing boats. The corvette had left the area, as did "Ro-34", recharging her batteries while heading out to sea at flank speed. She concluded her patrol with her arrival at Staring Bay on the coast of Celebes in the Netherlands East Indies on 7 March 1942.