PLANNING A TRIP TO SCAPA FLOW, I find myself talking to wreck-researcher Kevin Heath about the Admiralty trawler wrecks out of Kirkwall.
As an aside, Kevin asks whether I have ever dived the blockships at the Churchill Barriers.
My mind skips the part about the barriers, and at first I think he is talking about those wrecks scattered in Burra Sound - the Gobernador Bories, Doyle, Tabarka, Inverlane and their ilk.
Once we get that confusion out of the way, Kevin makes it clear that he thinks I should have a look at the blockships to the east of Scapa Flow, subsequently made redundant by construction of the Churchill Barriers.
In particular, in the bay outside barrier 2 that was once half of Skerry Sound, seven blockships remain. Whats more, if you carry enough gas and swim far enough, its possible to see them all on a single dive.
Seven wrecks in one - the idea gives the term wreck tour a whole new meaning. I just have to do it.
Which is how I find myself driving along behind the big white Scapa Scuba van as it heads up the hill from Stromness, cuts through the back roads behind Kirkwall, skirts the top of the Flow and crosses the first Churchill Barrier to the tiny island of Lamb Holm.
We arrive at the north end of barrier 2 to see bits of wreckage sticking out of the water.
My guide is Scapa Scubas Kieran Hatton, who dives the blockships regularly, both as a guide and as an instructor when using them as a training site.
For anyone who learns to dive with Scapa Scuba, there is a good possibility that every training dive will be on a different blockship.
A bit extreme, but its hard to think of a better starting point for a real UK diver.
To complete all seven wrecks on one dive, it helps to get the navigation sorted out before entering the water. So our arrival is timed to coincide with the early part of an incoming tide.
This way we can see bits of most of the wrecks just showing while clean water is flowing into the bay.

1 LYCIA
From the small pebbled beach by the end of the barrier, we begin with a wreck located right in the crook of where the barrier meets the beach.
The 2338 ton Lycia was a World War Two blockship, scuttled on 19 February, 1941. After the barrier was built next to the wreck, much of the hull was scrapped by Metal Industries.
The main wreckage remaining is an impressive engine and a few scraps of hull barely poking out of the sand. It is the top of the engine that stands clear of the water alongside the barrier. Next to the engine, Kieran wafts some stray kelp out of the way, and uses his glove to polish a section of brass tubing.

2 ILSENSTEIN
From the last few scraps of the Lycia, Kieran heads out on a bearing across the sand to the stern of the Ilsenstein.
All the guide-books and the Shipwreck Index agree that the Ilsenstein was scuttled on 18 February, 1940, to fill the gap left by the Cape Ortegal breaking up.
However, it seems that the rest of the data in the various books is a confusion of two or more ships, giving a size of 1508 or 8216 tons, built in Kiel or Belfast, one or two screws and engines, and built in 1889, 1895, 1898, 1904 or 1908!
Like the Lycia, the Ilsenstein was extensively salvaged for scrap once the barriers were completed, so accurate impressions of size are hard to get from the wreckage.
Nevertheless, it feels longer than the other blockships, and also looks considerably larger in photographs, so the 8216-ton size is the one judged more likely to be correct. That leaves the confusion of builders and dates to be resolved.
Hidden beneath the Ilsenstein are what little remains of the WW1 blockships Elton and Almeria, both extensively salvaged for scrap between the wars. As the dive only passes over these wrecks without revealing anything of them, they dont get counted for our 7 in 1 dive.
Above deck on the Ilsenstein, Kieran shows me a patch of black and white tiles from a bathroom floor. Some were salvaged by Italian PoWs to decorate the chapel they built nearby.
We then follow the port side forward to the railings on the capsized bow, resting all the way over on its port side.

3 EMERALD WINGS
From the Ilsensteins bow, the next wreck, parked almost bumper to bumper, is the 2139-ton Emerald Wings, scuttled on 5 July, 1940.
With all these wrecks following one after the other, you may well wonder how a newcomer to the dive like me could keep track of which was which. As we arrived at each wreck, Kieran would write the name in his notebook and hold it up for me to photograph the page. This gave me a reference to help me match photographs with wrecks later on.
The Emerald Wings is the wreck that stands furthest out of the water, its forward mast still in place, though at a slight angle.
The stern has collapsed in and slightly to port, while the rudder-post and steering quadrant are flat to the seabed. The propeller is standing behind, still attached to the shaft. Pairs of deck bollards are almost parallel to the seabed.
Further forward, a small derrick stands above a deck-hatch. The bow is all but submerged, the tide having risen since we began the dive.
With so much metalwork above the waterline at low tide, Emerald Wings is the least stable of the wrecks, so entering the remaining structure is probably not a good idea.

4 AC6
Having swum from end to end and back along the Emerald Wings, the next wreck is a floating crane pontoon barge, AC6, formerly used by Metal Industries in salvaging the various wrecks in Scapa Flow between the wars.
With the Admiralty wanting to close off the gaps between existing block ships as quickly as possible, the crane was removed and, on 22 May, 1941, the hull of the barge positioned between the Emerald Wings stern and the Argylls bow.
Designed to rest on the seabed to provide a stable platform for a big crane, the hull and support structure are remarkably intact.
Keiran worms his way though a canyon of massive upright girders to show me the boiler in the middle of the pontoon. The floating crane pontoon was a dumb barge, with no motive power of its own. The boiler provided steam to drive the crane mounted above.
We then continue with a similar wriggle through the girders of the other side. The overall ambience is more like diving below a pier than on a shipwreck.

5 ARGYLL
The Argyll had been visible from the shore as a boiler just breaking the surface. Under water, this boiler is all that stands any distance above the seabed. The rest of this 1185-ton WW1 blockship has collapsed almost flat, but that doesnt detract from the wreck.
Since it was scuttled on 17 September, 1914, the Argyll has not been significantly salvaged. The outline of the main deck is still there, complete with winches and bollards.
Behind the boiler, the Argyll disappears into the rocks of the barrier. This is the turning point of the seven wrecks route. From now on, each wreck brings us back closer to the beach.

6 CAPE ORTEGAL
We return through the floating crane pontoon and past the Emerald Wings stern to the stern of the Cape Ortegal, a 4896-ton steamship scuttled on 8 September, 1939 to fill a gap left in the decaying blockships from the WW1.
Unfortunately, the Cape Ortegal was not first loaded with ballast, so storms soon rolled the ship out of position and broke its back. The Emerald Wings and Ilsenstein were subsequently scuttled to finish the job.
Thanks to Kierans notebook I know which wreck we are on, otherwise I would have been completely confused by this stage.
With the wreck largely hidden beneath an upturned hull, the interesting bit is inside, where the mass of the engine holds the keel well clear of the seabed.

7 TEESWOOD
Back outside the Cape Ortegal, we head back along the full length of the Ilsenstein, then cross the sand to the Lycia and the beach. But we dont surface. There is still one wreck to go.
Continuing along the shallows of Lamb Holm to the east, we soon arrive at the stern of the Teeswood, a 1589-ton steamship scuttled on 17 September, 1914. The Teeswood was another unsuccessful blockship, drifting out of position as it sank, and ending up resting against the rocks of Lamb Holm.
Ninety minutes before, the propeller had been clear of the water. Now, with the incoming tide, it is submerged just far enough for us to dive on it. We follow the collapsed wreckage along the length of the ship and back, finding the prettiest bit of the entire tour right at the end.
Below the propeller, a curved section of the hull provides an arched cave, filled with bright orange-yellow dead mens fingers.
The dive has been conducted at a fair pace, hardly pausing for photographs as we zipped along and through each wreck. Diving seven wrecks in one hit, all shallow enough for entry-level training dives, is a unique experience.

Scapa Scuba is in Stromness (www.scapascuba.co.uk, 01856 851218). You can stay aboard one of the big charter-boats, or ashore in a local hotel or B&B (www.orknet.co.uk, 01856 872856). Northlink ferries operates services from Scrabster to Stromness and Aberdeen to Kirkwall (www.northlinkferries.co.uk,
0845 6000 449).


THE CHURCHILL BARRIERS
The accessibility of Scapa Flow to small ships though all the minor entrances had been seen as a danger to the Royal Naval fleet at anchor since before World War One.
While the big, deep entrance of Hoxa Sound was needed as the main route in and out for the fleet, and Clestrain Sound near Stromness provided a useful back door, the shallow entrances provided a sneaky way in for the opportunist commander of a destroyer, torpedo-boat or submarine.
A programme of blocking these entrances with scuttled ships - blockships - began in 1914, and was resumed in 1939 soon after Britain declared war on Hitlers Germany.
The torpedoing of the battleship Royal Oak by U47 on 14 October 1939 highlighted the danger. While the plans for sinking more blockships continued, a more permanent solution in the form of barriers to block the four small entrances to the east of Scapa Flow was initiated.
A system of barriers had been considered as early as 1915. In 1940, preparatory work began on the site, while models were constructed at the University of Manchester to look at how the proposed barriers would affect sedimentation inside Scapa Flow.
In 1942, a contingent of 1350 Italian prisoners of war were moved to Orkney to provide the labour force. The Geneva Convention prohibits use of PoWs for war work, so the official justification was the secondary use of the barriers as roads for the civilian population.
Suspended cables were used to drop gabions (steel-mesh baskets) of rock from above, and a small railway track built on the growing barriers was used to build up the sides with concrete blocks. Heavy construction was completed in September 1944, though the barriers were not officially opened until 12 May, 1945.