The Victorian Ships' Graveyard was the official dumping ground for Melbourne's unwanted hulls: an unregulated 'outer Heads' area used from about 1900, and from 1932 the proclaimed Commonwealth Area No. 3, a 6 km circle about 10 km south-west of Barwon Heads in 40–60 m. More than 46 vessels were stripped, towed out through The Rip and sunk with gelignite between 1913 and 1971, and all are protected historic shipwrecks. Don Diego was a three-masted iron barque of 320 tons, 44.4 m (145.6 ft) long, built by Scott and Co at Greenock in 1855 – the oldest hull in the Graveyard.

She traded to Australia under sail for nearly thirty years, ran aground off Queenscliff in 1874 and was salvaged, and in 1884 was cut down to a coal hulk in Melbourne. Thirty-two years later, on 26 May 1916, she was towed out past Point Lonsdale and scuttled in deep water, three years after the Brunette and long before the official ground was proclaimed. She lies in 70–72 m on the southern fringe of the Graveyard, the deepest of the barques and, at 2.6 km south of the Brunette, the most remote.

The Scuba Doctor describes her as well stripped and probably only a hulk on scuttling, with the bow and stern rising around 4 m from the seabed and the amidships lying flat – the characteristic profile of an old iron sailing hull that has folded outwards. The site is exposed and prone to the tidal currents that fan out from Port Phillip, and it lies near the main shipping lanes, so a dive needs slack water, a shipping check and a live boat. Deep-water sponges and sea whips, ling, boarfish and big crayfish are the expected inhabitants; visibility is often 15–25 m on the rare suitable days.

Don Diego is an expedition rebreather dive – 15 minutes at 70 m for well over an hour of decompression in a current-prone shipping approach – and has been dived by very few people. She suits only the most experienced Victorian technical teams, ideally in the same campaign as the Brunette, and is included here to complete the record of the Graveyard's oldest and deepest hulls.

Boat only. Charters leave from Queenscliff Harbour (Red Boats, Dive Victoria Group) or Portsea Pier (Dive Victoria Group, Bayplay); drive Melbourne–Queenscliff via the Geelong Ring Road and Bellarine Highway (about 1 h 40 min) or Melbourne–Portsea down the Mornington Peninsula Freeway (about 1 h 45 min). Private boats launch at Queenscliff (Larkin Parade) or Sorrento ramps; the wreck lies a few kilometres outside The Rip, so time the run through the Heads for slack or a following tide.

Boat time from Queenscliff is roughly 20–30 minutes and from Portsea 30–40 minutes in a fast RIB, longer in a displacement charter boat. Gear is loaded at the harbour; there is parking at Queenscliff Harbour and along Point Nepean Road at Portsea.

Fully exposed Bass Strait. South-westerly swell is the killer: most charters will not run on a forecast over about 1.5 m, and anything from the south or west over 2 m makes the site undiveable and the passage through The Rip dangerous. Northerly and north-easterly winds flatten the sea; a calm morning after several settled days gives the best visibility (often 15–25 m in autumn and winter).

Surge is felt on the wreck in any swell over 1 m. Tidal streams outside The Heads are weaker than inside but still run; charters aim for slack water at Port Phillip Heads or a favourable tide for the transit. Winter westerlies close the site for weeks at a time.

The wreck sits in or near the shipping approach and pilot boarding ground, so a shot line, surface cover and a delayed SMB are mandatory.

Expedition CCR dive at slack water: shot onto the bow or stern, which rise about 4 m from the seabed, run the flat midships to the other end and back in 15 minutes, and ascend the shot with 70–90 minutes of decompression under a live boat watching for shipping.

Technical (decompression) dive. Hypoxic or near-hypoxic trimix (e.g. 15/55 or 12/60) with EAN50 and oxygen; 15–20 min bottom time means 60–90 min of decompression. Rebreather divers dominate here; open-circuit needs multiple stages and a support boat with in-water support.

Drop a weighted shot on the wreck, use a delayed SMB from the wreck or a decompression trapeze under the boat; the site is in a shipping approach so free-drifting deco is discouraged. Slack water essential; shipping check with VTS.

No operator. Visited only by Melbourne technical/rebreather teams and Southern Ocean Exploration from private boats, typically once or twice a year at most.