'Na' (iii) was a Japanese submarine operation designed to intercept and destroy a significant element of the US Navy forces operating in the area to the north of New Guinea (April/May 1944).
The undertaking involved an eventual 25 submarines operating in a patrol line to the north of New Guinea and New Ireland. On 20 May a Japanese signal was intercepted and decrypted, revealing the Japanese plan for a submarine trap to the north of the Admiralty islands group to intercept an anticipated movement of US carriers. An initial group of boats, Ro-104, Ro-105, Ro-106, Ro-108, Ro-109, Ro-112 and Ro-116 of the 7th Submarine Squadron, established a patrol line across a route which ships of Admiral William F. Halsey’s South Pacific area command had used on two earlier occasions.
Thus alerted to the Japanese ambush plan, the US Navy despatched all available destroyer escorts to deal with the submarines, of which 17 were sunk. Among these US warships was the destroyer escort England, one of three ships of a specialised hunter/killer group: on 19 May she sank I-16 involved in a food-delivery run to Bougainville island and then, moving to the west against 'Na' (iii), sank Ro-106, Ro-104, Ro-116 and Ro-108 between 22 and 26 May before sinking Ro-105 on 31 May while operating as part of a carrier’s escort screen.