P.L.M. 24

During World War II the P.L.M. 24, after hitting a mine near cape Sepia, was stranded by his captain to save her on the Paltsi beach. After the war it was contracted to Mr. Marakis, a wreck salvager, and as a result most of the ship’s hull was cut as scrap, leaving only the lower part. Underwater Survey Team (UST) surveyed the remains of the ship and identified it through the archival sources available and with their own ship identification method called “geometric identification”.

The innovation of “cantilever” ships

Raylton Dixon shipyards were established in 1863 in Middlesbrough, England. In the year 1905, George Harroway and his son Waynman Dixon applied for a patent regarding a new type of ship structure, the so-called “cantilever”.

RayltonDixon as Mayor of Middlesbrough (Source: https://images.app.goo.gl)

The advantages of ships with cantilevers, are that the space of the holds is continuous, without tween decks, columns and unimpeded, while there are no additional dead spaces. These cantilevers at the upper two corners of the hold, contribute to its great structural rigidity and robustness, so that very heavy objects, such as railway equipment, can be carried on the deck.

The riveting method of beams according to the patent (Source: https://patents.google.com)

The dead space created by the triangular cantilevers is used as additional ballast tanks, auxiliary to the main ones. The shape of the hold being pyramidal, with the loading hatches placed in the center, helps to quickly load the coal and any other bulky cargo. As a result, there’s no need for cargo trimming, with all that it entails, as far as the saving of time and money is concerned.

This blueprint clearly shows the complete absence of vertical frames in the middle of the hold, characteristic of all ships of that era, as well as the two tanks on the top right and left (Source: https://patents.google.com)

The railway company P.L.M. and its naval fleet

During the early days of the steam age, many companies were led to the shipbuilding for the transport of passengers, goods and coal. Needless to say that the latter was extremely valuable for the movement of their marine and land based steam-powered fleet. Regarding the French companies, the main sources of supply of this precious commodity were the mines of northern France. Additional quantities needed, were imported from England and the Netherlands. However, at the outbreak of WWI, due to the great losses from the operations of German submarines, there has been a surge of fares from 10 francs per tonne in 1914, to 35 francs in 1915, 150 francs in 1917 and 180 francs in 1918. Remarkably enough, the price had not decreased in pre-war levels, since it stabilized at 100 francs after the end of the war. These high prices led to the building of collier ships, meaning bulk cargo ships for the transportation of coal.

Paris-Lyon-Mediterranee company logo (Source: http://www.phileas-fogg.net)

One of them was Chemins de fer de Paris à Lyon et à la Méditerranée, better known as P.L.M. This company was established after the merger of the companies operating on the Paris-Lyon and the Lyon-Marseille route.

Collage of company posters showing coverage in various destinations

The merger led to better service regarding the Paris-Marseille route, an axis that transported coal from the mines at the border with Belgium to the port of Marseille.

Paris-Marseille route. Above the first dot is Paris, third is Lyon and at the Mediterranean coasts, Marseille (Source: https://images.app.goo.gl)

Thus, the company decided to build colliers that are named after the initials P.L.M., accompanied by a serial number. These were built in two shipyards in Middlesbrough, according to the Harroway-Dixon patent and all of them were registered in Rouen, a town in the north of France, near the port of Le Havre.

Entry of Lloyds Register of Ships with every newly built vessels of this class (Source: Lloyds Register of Ships)

The small P.L.M.s with numbers from 12 to 17 were built at Smith’s Dockyards, with a length of 109 meters and a gross tonnage of 4,000 grt. The large P.L.M.s with numbers from 20 to 27 were built by Sir Raylton Dixon, with a length of 125 meters and a gross tonnage of 5,700 grt.

The P.L.M 16 was commandeered by the Germans, renamed PETER and sunk by the torpedoes of the British submarine VAMPIRE on September 22, 1944 between Skiathos and Pelion at great depth (Source: Musée national de la Marine)

As shown on the following blueprint, the differences are that large P.L.M.s have six holds, the loading and unloading cranes are reinforced and three additional structural elements have been added. Also, small P.L.M.s have triple-expansion engines, while the large ones quadruple-expansion engines, an innovation that is not found on similar ships, except in large ocean liners. Large P.L.M.s are among the first ships in the world to have steel hatch covers for the hold, as well as gear for mechanically opening and closing them.

Differences between small and large P.L.M.s (Source: Musée national de la Marine)

The fleet was managed by Societe National d’Affretement. A few months after winning French national elections, the ruling left-wing populist front decided to nationalize all railway companies under the SNCF, the French National Railways, which was set up on January 1st, 1938. The establishment of National Railways has not differentiated the way of fleet management, which continued to be managed by shipping companies outside the organization.
After the occupation of France by the German army, company’s fleet passed into the hands of the Vichy regime, the legitimate government with the blessing of the Germans.

The P.L.M 24 (Source: Jérôme Billard, La Mar Mar, la marine marchande française de 1914 à nos jours. ETAI, 1999)

On 5/9/1921, the steam collier P.L.M. 24 was launched at the Raylton Dixon shipyard in Middlesbrough, on behalf of the Paris-Lyon-Mediterranee railway company, while on 17/12/1942 it was requisitioned by the Germans in Port de Bouc, renamed PERIGORD and transferred to the management of Deutsche-Mittel Meer Reederei. Despite its renaming, the ship was still referred to as P.L.M. 24.

The P.L.M. 24 (Source: http://uim.marine.free.fr)

The birth of the GRAMPUS Class minelaying submarines

By the end of World War I, Royal Navy started doing research with a view to building a minelaying submarine with more advanced features, as compared to those active during the war, which could carry only 20 mines. In 1927, the M3 submarine was converted into a prototype minelayer.

The HMS M3 in its original form with the huge 300mm deck gun (Source: https://images.app.goo.gl)

For the first time in history, this model used mines on trails located in a compartment on the outer hull of the submarine, throughout almost its entire length.

The M3 submarine after the addition of the mine transport compartment. The launch hatch is visible on the stern, while the transport shell does not extend over the entire length to the stern (Source: Archive of UST)

From this compartment, mines were released from a hatch at the stern. This was done by means of a conveyor belt equipped with a chain, a very simple structure with rails and a drive motor on a chain-conveyor.

Photo of the mine release mechanism facing the stern and the release hatch (Source: HMS RORQUAL Commanded by Lennox Napier DSC DSO June 1941-December 1943)

Various tests led to the design of GRAMPUS class minelaying submarines in 1932, six of which were manufactured. Their hull was similar in structure to the PARTHIAN class submarines, one of which, the HMS Perseus, can be found submerged in Cephalonia.

Launching of the HMS PORPOISE and then the HMS GRAMPUS from which the class was named after. A main feature is the very high profile of ships along the length and not only in the area of the tower, as a result of the mine transporting hull. (Source: British Pathe)

The main weaponry of these submarines consisted of 50 MK XVI contact mines, a modified version of MK XV, with a maximum operating depth of 180 meters, due to the lighter outer shell of the mine.

The MK XVI mine (Sourcebook: Handbook of MK XVI mine unit, 1934)

Loading of MK XVΙ mines on the HMS NARWHAL, a GRAMPUS class submarine, from the stern hatch (Source: https://doriccolumns.wordpress.com)

The HMS RORQUAL submarine

HMS RORQUAL, the most successful minelaying submarine of WWII and the only one of the GRAMPUS class, was launched on 21/7/1936 and managed to get through the war intact. Its operations caused the sinking of ships weighing a total of 57,000 tons, about 36,000 of which sunk by its mines. HMS RORQUAL had laid an impressive number of 1.284 mines in total.

HMS RORQUAL (Source: UST Archive)

After the Royal Navy has manufactured a mine that could be deployed from the 21-inch torpedo tubes of its submarines, the need to build specializedclasses of minelaying submarines has been eliminated. However, the GRAMPUS-class submarines, apart from the minelaying missions during WWII, also undertook supply missions, the so-called “magic carpet”, with great success during Malta’s naval blockade from the axis forces in 1941-1942. HMS RORQUAL was the first to carry out such a mission, followed by eight other successful ones.

The crew of HMS RORQUAL along with Captain Napier on the right-hand side of the mine’s patch on the Jolly Roger. In the photo, we see the “custom of showing off” Jolly Roger. The pirate flag appeared after the end of each successful mission. The photo shows the 965 mines that have been laid so far, the number of ships sunk by torpedoes represented with horizontal lines, as well as the three stars corresponding to ships sunk by its cannon (Source: HMS RORQUAL Commanded by Lennox Napier DSC DSO June 1941-December 1943)

The mine storage compartment served as a transport area of valuable supplies for the besieged, mainly fuel for planes in Malta and ammunition. During these specific missions, any free space in its internal compartments was used for the transport of materials and food, which should not come into contact with water.

As shown in the photo, the mine transport shell has been removed to facilitate cargo loading. In this specific mission, the 40mm Oerlikon anti-aircraft transport took place, as well as the jeeps that would tow them. The transfer occurred at the island of Leros, which was besieged by the Germans. The weapons were an unpleasant surprise for the German pilots who descended too low for strafing, not expecting any antiaircraft resistance from the defenders. (Source: HMS RORQUAL Commanded by Lennox Napier DSC DSO June 1941-December 1943)

The mine-laying of HMS RORQUAL in the Skiathos-Pelion Strait

After the defeat of the German forces in North Africa on May 13th, 1943 and their subsequent withdraw, HMS RORQUAL was transferred to the area of operations of the Aegean Sea. In this marine area, traffic was still sufficient due to the supplying of the occupying forces through the axis of Romania’s oil wells in the Black Sea and through the Dardanelles Straits in the Aegean Sea.
On May 29th, 1943, the Greek submarine “Y-1 KATSONIS” was on a patrol. At 16:15, it spotted a steamer in the Skiathos Strait, adjacent to Lefteris reef. The submarine fired two torpedoes and the ship trying to avoid them, landed near the coast of Cape Sipia. After multiple shots fired with its cannon, as well as another torpedo that crashed on the side of the ship and did not explode, the crew of KATSONIS captures the Spanish captain, as well as four Greek members of the crew.
The Spanish cargo steamer requisitioned by the Germans was the RIGEL.

The cargo steamer RIGEL (Πηγή: https://www.wrecksite.eu)

After interrogation of the crew about the routes of the German ships from Thessaloniki to Piraeus, the information transmitted to the English allies indicated that the strait between Skiathos and Pelion should be mined, with Cape Sepias being the most likely crossing point.

Investigation report of the RIGEL crew concluding the need to mine Skiathos Strait (Source: ADM 267/124)

English staff officers, in their correspondence, left to Napier’s discretion, commander of RORQUAL, the site selection for mine-laying.

The report with the location to be mined according to the staff officers, although the exact spots were left to commander Napier's discretion (Source: ADM 267/124)

On June 25th, HMS RORQUAL departed from Haifa for its 21st war mission and on July 2nd laid 29 mines at Cape Possidi, while the next day headed towards the Pelion-Skiathos Channel.

The mine-laying report (Source: ADM 267/124)
The map of RORQUAL’s 21st war mission with the mine-laying spots from its war log (Source: ADM 267/124)

The sinking chronicle of P.L.M. 24

At that exact spot, it laid the remaining 21 mines at 09:57, 5.1 N.M northwest of Cape Sepias for 1.5 NM and with an approximate distance between them 130 meters. HMS RORQUAL ended its patrol on July 14th.

Illustration of the minefield according to RORQUAL’s log (Background: Google Earth – Source: UST Archive)

On September 2, the 23rd mine laying mission would begin in two locations. The first is in the Trikeri Strait on September 9th and the second north of Skiathos on September 10th. During the mine-laying, the existence of a shipwreck on the shores of Pelion was noticed.

Chart from RORQUAL’s log with the mine-laying spots and the shipwreck sighted as well (Source: ADM 267/124)

According to the report written by the commander of RORQUAL, the unidentified ship had stranded on the rocks of the coast with the stern fully submerged.
As the ship was at a distance of 2 NM from the last RORQUAL’s laid minefield, and in the absence of other attack information in the area, this success was credited to RORQUAL.

Report of shipwreck sighted (Source: ADM 267/124)

According to the German report on September 8th, a notice arrived at the Harbormaster of Volos mentioning that the P.L.M. 24 was sunk by two torpedoes the day before. Obviously the reference to the reason of sinking is wrong, since it was impossible to ascertain whether the ship was sunk due to a mine or a torpedo.

P.L.M. 24 sinking report in German archives (Source: Published with the permission of Byron Tesapsides)

According to locals, the ship, after hitting the mine, stranded and washed ashore. The crew disembarked and climbed the mountain, where the partisans found them and killed them. Until the early 1950s, the ship was still there and mostly outside of water. Then, contractor Mr. Marakis began its hoisting and managed to pull it out almost completely. Needless to say that this ship, with most of its part outside the water, was a divine gift for the inhabitants of the area, who were struggling to survive amidst the occupation. As a result, people stripped off its various usable materials, as well as everything that could be sold.

A plate from P.L.M. 24 (Source: UST)
Aluminum table from P.L.M. 24 found at a backyard in the village of Paltsi, Pelion (Source: UST Archive)

Geometric identification of P.L.M. 24

Historical and archival identification was followed by the geometric identification developed by the Underwater Survey Team and applied to the P.L.M. 24 shipwreck. This process includes the following 3 stages:

  1. data collection, where the research and pursuit of the ship’s blueprints and the topographic/photogrammetric surveying of the wreck are carried out;
  2. rectification of the blueprints, where they are being scanned and their colors, image and scale are corrected, so that they can be handled like maps, i.e. measurements can be made on them, and
  3. matching of plans, where the survey plans are compared to the blueprints.

The advantage of geometric identification compared to the other methods of O’Shea (2004) and Ahlström (1997) is that it constitutes an evidentiary method, because it is based on actual measurements. That very fact gives it validity and provides the evidence for identification. On the basis of this evidence, it confirms or denies the historical and archival identification that has been made in a shipwreck.

The P.L.M. 24 shipwreck is located on the shores of eastern Pelion at Paltsis beach, about 50 Km away from Volos. More specifically, it lies next to a rock about 500 meters southeast of the Paltsi beach at a maximum depth of 12 meters. The wreck was blown up and most of it has been salvaged.

Shipwreck site of P.L.M. 24 (Background: Google Earth – Source: UST Archive)

Two dives were carried out, one for filming and another for the survey and photo shoot of the wreck. There were found five distinct parts that survive up to date as follows: bow, left, central, ballast tank and stern section. Two GPS coordinates measurements were taken from the surface, one on the bow and one on the stern. These showed that the total length of the wreck, which is about 120 meters long, is an exact match with the blueprints.

The separate parts of the P.L.M 24 shipwreck (Source: UST Archive)

The result of the survey and the photo shoot is the production of photomosaics and 3D digital models with photogrammetric methods for each of the individual sections. This process enables us to obtain the necessary layouts for use in geometric identification. Last but not least, video footage was used to produce a short film about the wreck.

Photomosaics and 3D models taken from the separate parts of the P.L.M 24 shipwreck (Source: UST Archive)

Only the bottom part with its structural elements survives from the bow section. It is 30 meters long and 8 meters wide. There has been made a photomosaic for this specific part.

Photomosaic and photo of the bow section of the P.L.M 24 shipwreck (Source: UST Archive)

In addition, there has been made a 3D model for the left section of the wreck, from which its layout was exported. It is 37 meters long and 2 meters wide.

3D model and photo of the right section of the P.L.M 24 shipwreck (Source: UST Archive)

Α photomosaic for the central section is also available. It is 25 meters long and 10 meters wide.

Photomosaic and photo of the central section of the P.L.M 24 shipwreck (Source: UST Archive)

One of the elements used for geometric identification is the ballast tank. For this purpose, we created a 3D model from which its layout was exported. It is 29 meters long, 2.5 meters wide and 2.8 meters high. It’s worth noting that this is the only part of the wreck that can be penetrated by a diver.

3D model and photo of the ballast tank of the P.L.M 24 shipwreck (Source: UST Archive)

Another element used for the geometric identification is the rudder, which is located at the bow section. Once again, there has been made a photomosaic. The piece to the right of the photo is the rudder, while the round beam protruding is the rudder stock. Το πρυμναίο τμήμα έχει μήκος 15 μέτρα και πλάτος 12 μέτρα.

Photomosaic and photo of the bow section of the P.L.M 24 shipwreck (Source: UST Archive)

In order to carry out the geometric identification, apart from the survey, the ship’s blueprints were also needed. Due to we didn’t manage to find blueprints from P.L.M. 24, we used the relevant data from P.L.M 16, which are almost identical. P.L.M. 24 is 125 meters long, whereas P.L.M 16 is 109 meters. The image on the left shows the side views of the P.L.M. 24 scale model located at the Maritime Museum of Paris and on the right, the blueprints of P.L.M. 16.

Side view of the P.L.M. 24 scale model and the blueprints of P.L.M. 16 (Source: Musée national de la Marine)

What is more, side views of P.L.M. 24 and the blueprints of P.L.M. 16 were compared, after their rectification, in order to determine whether these two ships are identical and to what extent. As shown in the figure, the three green frames define the points at which the two ships differ substantially and the sum of their length is the difference of 16 meters between them. It has thus been concluded that blueprints from P.L.M 16 can be used to identify P.L.M. 24.

Comparison between side views of P.L.M 24 and blueprints of P.L.M. 16 (Source: UST Archive)

Due to the fact that the wreck is not preserved in its entirety, the geometric identification was applied to three characteristic features of the ship that still lie on the seabed. For this purpose, we have used both details of the side view and the cross section of the ship’s “anatomy” compared to relevant photographs and collages of photographs of the wreck, as well as details of the side view of the ship’s scale model compared to photographs of the wreck.

The first feature is the ballast tank. The rectified photograph of the entrance of the tank was taken on the basis of measurements and we compared it with the cross section of the blueprints. There is an exact match of the photo and the design, i.e. shape and dimensions correspond to each other.

Matching of the ballast tank at the shipwreck with the blueprints (Source: UST Archive)

The second characteristic feature is the rudder. Here, photographs of the shipwreck’s rudder were edited and rectified on measurements. Then we compared them with the side view of the rudder, based on the blueprints. There is an exact match at every point, such as shape, axis, dimensions of the scantlings and the gaps between the scantlings.

Matching of the rudder at the shipwreck with the blueprints (Source: UST Archive)

The third and final feature is the bollard. The photograph taken from the wreck and the photograph from the scale model of the ship were compared and, as shown in following the picture, they are the exact same. This bollard is very distinctive. Despite the thorough research, nowhere else has been found a similar bollard on a ship, which makes it a unique and at the same time indisputable proof regarding the identification of the shipwreck.

Comparison between the bollard from the scale model with the actual bollard of the ship (Source: UST Archive)

Taking all the above mentioned information into consideration and despite the damage done to the wreck, we are safely led to the geometric identification of the P.L.M. 24 shipwreck.

The P.L.M. 24 shipwreck video on the Paltsi beach was edited by Nikos Sidiropoulos.


British National Archives

Lloyds Register of Ships

Musée National de la Marine, Paris

German Archives

Naval History Department


Ahlström, C., 1997. Looking for Leads: Shipwrecks of the Past Revealed by Contemporary Documents and the Archaeological Record. The Finnish Academy of Science and Letters, Helsinki.

British submarines 1939-1945, Osprey publishing, Innes Mccartney.

Coasters: An Illustrated History, 2020, Roy Fenton.

Jérôme Billard, La Mar Mar, la marine marchande française de 1914 à nos jours. ETAI, 1999.

Mines, Minelayers and Minelaying, 1951, J. S. Cowie.

O’Shea, J. M., 2004. The Identification of Shipwreck Sites: a Bayesian Approach. Journal of Archaeological Science, vol. 31, pp. 1533-1552.

RORQUAL Commanded by Lennox Napier DSC DSO June 1941-December 1943.

The Encyclopedia of Weapons of WWII: The Comprehensive Guide to over 1,500 Weapons Systems, Including Tanks, Small Arms, Warplanes, Artillery, Ships, and Submarines, 2002, Chris Bishop.

Internet Sources





Additional records
Attack report from Y-1 KATSONIS submarine and the grounding of RIGEL (Source: Naval History Department)
Author: Nikolaos Sidiropoulos

Ο Νικόλας Σιδηρόπουλος γεννήθηκε στις 28/6/1977 στην Θεσσαλονίκη. Το 2002 πήρε το πρώτο αστέρι της CMAS και ξεκίνησε την ενασχόληση του με τις καταδύσεις. Ασχολείται με την ιστορική και αρχειακή έρευνα της ομάδας, καθώς και την υποβρύχια βιντεοσκόπηση.