tangle of cables and green ambient light filtered though the tower's viewing slits, from where the captain would oversee the battle. When I first dived the Karlsruhe 20 years ago the bow was magnificent; both guns and capstans and the bow itself were completely intact. Ten years later, the guns had started to collapse onto the sea bed. But what I saw on my most recent dive was rather sad. Both guns had fallen to the sea bed, exposing their magazine shafts. The capstans were also on the mud and the bow had completely disintegrated, the armoured deck having peeled away from the collapsed hull. I hoped the deeper wrecks had fared better.Lying at a maximum depth of 35m, the Brummer definitely warranted the use of nitrox, and I used a 30 per cent mix. This gas reduced the nitrogen content to a level where narcosis was not an issue; trimix was an option, but a dive of this depth didn't merit the cost. The shot-line on this dive was so busy with travelling divers that it could have been a scene from Thunderball, were it not for the disappointing visibility of about 4m. I reached the hull just aft of the bridge, and was glad to see that the railings on the bridge were still intact. It is now the only light cruiser in the Flow to display this feature. Continuing to the bottom I finned forward with the vast bridge structure intact above me. It was an amazing sight, even in the poor visibility. Then the armoured control tower came into view, with its rangefinder still in place on top. Adorned with orange and white plumose anemones and surrounded by a school of small fish, this was a slice of Scapa at its best. Even the visibility picked up, and the scene was suffused with gentle green light - fantastic!Further forward, I noted a gun lying on the sea bed. As the Brummer only had a single gun forward of the bridge, this was bad news. The forward deck gun that used to sit with its barrel pointing at a jaunty 45-degree angle towards the surface had now collapsed onto the bottom. It looked as if the deterioration of the Brummer's bow I had noted on my last visit had continued. Nitrox mix or not, my computer was letting me know that I was now into deco. I decided to move up to the port side of the hull and let the rows of portholes guide me back to the shot-line. While the bow gun was a disappointment, the Brummer's bridge and control tower should not be missed as they are superb features.Next up was the battleship Kronprinz Wilhelm. This huge lump of steel had never provided me with a dive that was as exciting as the light cruisers. These ships were so large that it takes a number of dives to figure out where you are. I used a 28 per cent nitrox mix, as I was on a mission to view the main armament on this massive wreck. As the battleship lies upside down, I had to journey to the sea bed at 40m, hence the light nitrox mix - had I wanted a long bottom time, trimix would have been preferable, but I didn't need to be down there too long. As I went down the line, the hull of the inverted battleship loomed out of the 6m visibility. Reaching the bottom, I found a dark opening and entered the wreck. The teak deck stretched above me and I noted a large mooring bollard with cables fused around it, then a wall of steel formed by the main turret. Finning aft, the barrel of the main gun took shape. It was a long fin along to the muzzle, then to the aft turret and its barrel, which had crashed through the decking. The Kronprinz Wilhelm was my most rewarding dive of the trip so far. There was plenty to see on the hull on the way back to the line for our deco stops. I had opted to take along a stage cylinder of 50 per cent nitrox to accelerate my decompression.All good fun, but the next day, I was keen to use a 26/23 trimix for a 44m dive on the James Barrie. Back in the day, divers would plan a day off on Wednesday when on a Scapa trip. Midweek bends became a regular occurrence before the effects of repetitive deep diving were understood, but the advent of dive computers and nitrox mixes has done a lot to reduce this problem. The line went down a long way and, as we were outside the Flow, the visibility was a beautiful 20m. The wreck soon came into view. Nothing is ever perfect, however: slack water had failed to transpire, and to compound this problem, three boats had decanted their divers into the water at the same time. Landing at the stern, I finned along a companionway and found shelter in a hold. I watched divers fighting the tide to move forward to the bow. I finned past the engine room to the bridge, before deciding to throw in the towel and drifting back to the line. Even while working hard below 40m, my head was clear as a bell.If only the water was as clear the following day. On my way down to the battleship Markgraf the visibility was back to a murky 5m. We landed at the stern and finned past slabs of armour plate that had fallen from the hull. One easily identifiable feature was the massive rudder, which we investigated at the end of the dive. I could feel the benefits of the helium in the 25/23 trimix; at well below 40m, my thoughts had a clarity that was sadly not reflected by the visibility. I ascended back up the line very slowly to let the helium out of my system, ready to complete my deco stops once again on 50 per cent nitrox.The last day of the trip had arrived and my favourite Scapa wreck was on the menu: the Köln, the most intact of the light cruisers. Even though the maximum depth is only 36m, I decided to use a light 23/23 trimix to experience the benefits of this breathing mix on a shallower wreck. The dive profile was almost identical to that of the Brummer earlier in the week. I dropped down the line and was pleased to note that the water was green rather than black and the visibility had crept up to a respectable 7m. Following the line down to a lifeboat davit just behind the bridge, I dropped down the back of the bridge to the sea floor and, for the first time, noted a large 'For Sale' sign. I hadn't a clue how on earth it got there. Moving forward, I enjoyed looking at all the intricacies of the bridge and noted the large mast running out above the sea floor. I couldn't remember ever seeing this before - perhaps my attention had always been focused on the bridge, or more likely I was feeling the benefits of the helium-rich narcosis-reducing trimix (try saying that when you're narked!). Just at the front of the bridge structure was the armoured control tower, with its large T-shaped rangefinder on top. I could just make out the viewing slits through the dense coverings of plumose anemones. This was incredible diving and, unlike the Brummer, the bow hasn't disintegrated. I was especially glad to spy the deck lights, which I had never seen before. Forward again, and the massive capstans came into view, surrounded by great links of chain that stretched away to the hawse pipes. Then I saw the mooring bollards and the prow itself. The bow was still intact, though greatly encrusted with more anemones.Twenty-five minutes into the dive, I followed the deck edge and viewed the scene from the shallower side before eventually locating the shot-line on the davit. I switched to my 50-per-cent nitrox mix to decompress and reflected on the magnificent dive I had just enjoyed. If you're looking for reasons to do an entry-level trimix course, the Köln is as good a reason as any. Thanks to Gordon Mackie of GM Diving for organising a marvellous tripThe wrecksKarlsruheDepth: 20-27mGas: airShallowest of the light cruisers, this is the most popular shakedown dive, with even more to see as the wreck is now breaking upBrummer Depth: 24-36m Gas: nitrox 30Regarded by many as an unmissable dive, this 140m-long light cruiser is known for its bridge and deck gunKronprinz WilhelmDepth: 12-40mGas: nitrox 28The most intact battleship; main armament can still be seen at sternMarkgrafDepth: 16-46mGas: trimix 25/23Deepest battleship; look out for casement guns and rudderJames BarrieDepth: 36-44mGas: trimix 26/23Fantastic, intact trawler, often in 20m visibilityKölnDepth: 24-36mGas: trimix 23/23The most intact of the light cruisers. Highlights include bridge, control tower, and intact stern with guns 
