HNLMS K XI was the lead boat of the Dutch Navy's K XI class of colonial submarines, ordered in 1919, laid down at the Fijenoord yard in 1922 and commissioned in 1924. The K stood for Koloniaal: these boats served in the Dutch East Indies. In December 1941 she attacked Japanese landing forces off Malaya, and she rescued 13 survivors of HMAS Yarra. She later served under British command from Colombo and, from February 1945, under US command from Fremantle. Declared obsolete in May 1945, she was handed to Australian authorities for salvage.

While being stripped alongside North Wharf in Fremantle on 28 March 1946, she sank in 14 m. Salvage diver Hillary Malone spent months sealing 310 openings before she was refloated on 28 June 1946, and she was reportedly scuttled in September 1946 near the Rottnest ship graveyard. Her true position remained unknown until 1 January 2025, when Andrew Oakley (WreckSploration), David Jackson (Diving Western Australia's Shipwrecks) and Patrick Morrison (WA Museum) found her about 15 km from the recorded site using aerial magnetometer and side-scan sonar surveys. The WA Museum formally identified her in February 2025.

The 66.7 m hull lies on sand in 38 m, bow to the north-west. Roughly three-quarters is below the seafloor, with the stern sunk about 3 m. Visible features include the large flange where the conning tower was removed, the aft crew hatch, two cut-away sections exposing machinery, and four forward torpedo tubes. Coral growth covers the structure, and the steel has little integrity left.

The K XI is a protected heritage wreck and a new work-up site for Perth technical divers.

Launch at Woodman Point boat ramp (about 13 nautical miles to the site) or Leeuwin Boat Ramp in East Fremantle. The wreck lies at S 32°09.023' E 115°29.968', about 8 nautical miles west of Carnac Island and 7.8 nautical miles south of Rottnest, in open ocean with no nearby land for shelter. Allow 40–60 minutes each way.

Anchoring on or near the wreck is prohibited; use a drop shot and live-boat pick-up. Charters are run by Image Dive, Perth Scuba, the UWA Dive Club and Bucket List Diver.

Exposed offshore site with no protection from land. Needs light winds and low swell for the long run and live-boat operations; swell can sometimes improve visibility. Current has been reported running east to west but varies.

Plan to be off the site before the afternoon sea breeze. Check conditions on vis.report.

Descend the drop shot to the sand at 38 m, follow the hull from the bow (facing north-west) along the conning-tower flange, the aft hatch and the cut-away machinery sections to the buried stern, then return. On nitrox 28%, no-decompression time is about 11 minutes; technical divers plan staged decompression. Ascend on a DSMB for live-boat pick-up.

Divingwawrecks describes it as a recreational-limit dive at 38 m but recommends technical decompression diving for thorough exploration; trimix or EAN plus deco gases; rebreathers suitable. Drop shot and live-boat operations only.

Image Dive & Charters, Perth Scuba, UWA Dive Club and Bucket List Diver run occasional charters for technical and experienced deep divers since the 2025 discovery.