Anatomy of a submarine wreck
Appeared in DIVER September 2007
Tired of swimming over wrecks that consisting mainly of smashed iron plating and boilers? Submarines are the answer, says Innes McCartney, whose specialist guide is illustrated by Rico Oldfield, with additional photos by Patricia McCartney and John Liddiard
AS I TRAVEL THE COUNTRY diving submarine wrecks, I find that divers are enthusiastic yet can find it hard to make sense of the wrecks they dive, identify key components and know what to look for, especially on unidentified wrecks.
I want to equip divers with the knowledge to get the most out of diving on the true raiders of the deep.
British divers are blessed with many thousands of shipwrecks, and among them are hundreds of submarines. Those around the UK are mainly German or British, the German subs lost mostly in wartime and the British in peacetime.
Submarines make interesting dives for several reasons. They are usually very intact, looking much as they did when they sank.
Most are small enough to get around on one dive, and they have many interesting features to examine. In most cases, the story of the submarines life and death is as exciting as it is often tragic.
And for those divers who enjoy the thrill of identifying a wreck, many submarine wrecks have still to be properly catalogued and identified.
How did it originally look ?
Everyone knows that a submarine is long and has a conning tower sticking up in the middle. However, there is more to submarines than may meet the eye. They have been built for many different purposes over the past 100 or more years.
The M2, for example, sunk off Weymouth, was fitted out as an aircraft-carrying submarine when it sank, so part of its conning tower incorporated an aircraft hangar. The M1, off Start Point, was equipped with a 12in gun from a battleship. These are two extreme examples of the submarine concept.
Submarines were usually built to do three things - torpedo ships, shoot at ships with a deck gun, and lay mines.
Some could do all three. The German WW1-era UCII-Class, such as UC65 sunk off Eastbourne, is one such example. Most submarines sunk around the UK will have at least one or two of these features.
Sub wrecks around the UK can vary dramatically in size. British K and M-Class vessels are huge, while the little Holland 5 (a protected wreck off East Sussex) or British A-Class submarines are tiny.
A good way of getting to grips with the sub you plan to dive is to study a photo, or a drawing of the class. From these it should be possible to see how many torpedo tubes it had, whether it carried a deck gun, and whether mines were laid from chutes built into its superstructure.
The location and number of all of these features will help you to orientate yourself while on the wreck.
Other distinguishing features regularly seen on photos of submarines include the number of propellers, rudders and hydroplanes, periscopes, communications gear, hatches, anchors, bridge equipment, sonar domes, snorkels and anti-aircraft guns. Such features will differ from class to class and help train you to see the submarine in its various shapes, sizes and configurations.
When I started to dive, all I knew about ships (let alone submarines) was that they had funnels!
I soon realised that a better knowledge of marine architecture would enliven my diving. The same applies to submarine wrecks, with one major advantage - they are mainly upright and intact, and look like the photos in the books!
How sub wrecks break down
More than any other vessel, submarines are constructed to withstand the pressures of the sea. Its a good thing for wreck divers that subs are so tough, because they hold their basic shape very well.
A submarine normally has a pressure hull, a toughened steel cylinder inside which the crew live. Alongside this is housed all the operating equipment.
Pressure hulls are generally made of high-strength steel and invariably remain intact for decades. The Holland 5 (sunk in 1912, the same year as Titanic) looks as it did the day it was launched!
Outside the pressure hull there is usually an outer skin of thinner metal to give the sub a hydrodynamic shape, a deck and a bridge from which to con, or direct the steering of, the submarine when it is running on the surface.
It is this thinner metal that tends to corrode over time. Under the deck, in the bridge and in the outer skin is much external equipment that will eventually fall away.
The keel is where the batteries (for underwater propulsion via electric motors) are stored. Lead batteries are heavy, which is good news for divers because it means that when submarines sink they dont roll over - ever.
The keel shape is not flat, however, so many submarine wrecks tend to lean over at around 45. For some reason Ive never worked out, most U-boats (the term for a German submarine) seem to lean to port.
So, when a submarine starts to corrode, the equipment stowed and mounted externally around the outer skin, in the bridge and under the deck, will fall off and land on the seabed on the side to which the submarine is leaning.
Every submarine wreck you dive will be going through this process, so swimming along the seabed on the side towards which it leans will lead you to find much debris.
The other side will be clear and fairly boring. This has led many an inexperienced diver to swim the length of a sub wreck and conclude that it is a barge! So if youre looking at a clean hull and smooth seabed, explore the other side of the wreck.
Within the debris field will be many items worth seeing, but much of the really interesting stuff will still be firmly anchored to the pressure hull, or poking out through it.
A submarine wreck contains all the information needed to tell you what it is, without the need necessarily to bring items to the surface. The number and disposition of items will always allow an accurate assessment of the class of submarine. If the identity is known,
these items will add to the enjoyment of the dive.
LOOK OUT FOR:
Deck guns were placed on submarines in an era in which single targets of opportunity could be engaged while at the surface and unlikely to sustain damage. Many more shells than torpedoes could be carried, vastly increasing the destructive capability of the submarine.
In the WW2 era U-boats began to operate regularly inshore, and the guns were removed as vulnerable targets became rarer. Often a ready use ammunition locker will be found close to the gun. Calibres generally range from 45 to 105mm, and, as a rule of thumb, the larger the calibre the later the loss date.
The presence of 20 or 37mm guns can point to the submarine being of late WW2 vintage. When deck guns were removed from U-boats, they were replaced with AA guns for fending off aircraft. AA guns are unique to U-boats sunk after the summer of 1943. They generally fall off the submarine and are found in the debris field.
Some are mounted externally on the casing, but most will protrude from the pressure hull.
Commonly the bows of a submarine wreck will have four torpedo tubes. The most common types of U-boat, the WW1-era UBIII Class and WW2 Type VII Class, have four forward and one after tube.
Any submarine you dive with a different configuration will be rare and noteworthy.
Torpedo tubes are easy to spot when the outer skin has rotted away, because they protrude from the pressure hull. If the skin is intact, its best to look for the outer torpedo doors that give the streamlining to the submarine.
The latter is angled at around 45 to the deck to facilitate sliding the long torpedo into the submarine, and all submarines will have one forward of the conning tower.
Such a hatch aft of the conning tower indicates the presence of an aft torpedo tube or tubes.
The location of access hatches on the decks varies from class to class and is a key identifier. Looking down through the open hatch into the submarine can often tell you what the hatch was mounted above - the torpedo room, for example.
Hatches can be found open or closed. This can indicate the circumstances of the loss of the vessel, although corrosion of the locking mechanism must be considered.
The presence, location and number of mine chutes is a very good way of identifying a class of submarine. It will invariably be the German UCII-Class minelayer, which was active in UK coastal waters in WW1. Several were lost around the coast and make very interesting dives. The British L24 off Weymouth was fitted with mine chutes, as were U218 off Malin Head and U214 off Start Point. These rare features are worth examining thoroughly.
Propellers and rudders
The presence of a single rudder or single hydroplane aft is also noteworthy. Most submarines have a hydroplane and rudder for each propeller. Hydroplanes are also found on the forward section of the submarine. Squarish ones tend to be German, roundish ones British. British submarines could fold their forward planes away, unlike the typical U-boat.
The presence of a snorkel identifies a wreck as a late WW2 U-boat. This device appeared in 1944 and was fitted to keep submarines constantly submerged. They are commonly seen on Type VII U-boats sunk around the UK.
Of note is the sorbothane covering on the float, designed to absorb radar waves - the first true stealth technology!
Combat damage is usually easy to contrast against accidental damage by trawls. Depth charges can cause substantial damage if detonated close; Hedgehog damage is invariably on the top surfaces; and if the submarine is in two halves, assume that it has been torpedoed.
A lack of damage indicates either a diving failure or a sub lost on tow to the breakers.
Submarines usually carry two periscopes. The attack periscope is small, designed to be difficult to spot when deployed. The observation periscope is much larger and more intricate.
Both will be in the area of the conning tower, and when the marine growth is wiped off, the lenses and bronze housings can look very nice and are worth a photograph. Extended periscopes are rare on wrecks but can indicate what the sub may have been doing when it sank.